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Ben Nadel at CFUNITED 2010 (Landsdown, VA) with: Randy Brown and Rick Mason
Ben Nadel at CFUNITED 2010 (Landsdown, VA) with: Randy Brown Rick Mason ( @Rick_Mason )

Attempting To Inject My echo.log() CSS-Styled Logger As A Chrome Extension

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Last week, I had fun creating a Chalk-inspired echo library that allows for CSS-formatted console logging. It leverages the %c string interpolation feature of the Console API in order to apply simple styles to a given log message. To make this echo library even more usable, I wanted to see if I could inject it into the page as a Chrome extension. This would truly make it a "drop-in replacement" for console.log() and remove the friction of having to load the echo.js JavaScript file in my application code. I've never actually built a Chrome extension before; so, I wanted to see if I could create an MVP (Minimum Viable Product) for myself.

View this code in my Echo-Log MVP project on GitHub.

Chrome browser extensions seem super robust. A quick glance at their sample extensions repository, and you can see just how much functionality can be packed into an extension. Ironically, the one thing that I'm trying to do - modify the window object - seems to be the one thing that they don't want to make very easy. Again, having zero experience here, it looks like they want Chrome extensions to run with a lot of isolation, which I guess means blocking access to the window object?

Thankfully, I came across this StackOveflow post, which described a possible path forward. While we can't modify the window object from within one of our "extension scripts", we can modify the window object directly within a "content script". This sucks for modularization (ie, splitting files up); but, at least it works for my MVP.

A "content script" is a JavaScript file that Chrome will automatically inject into the embedding page at different life-cycle moments. From within our content script, we can programmatically define <script> tags that contain JavaScript code that augments the window object. For example, we could define a content script that looks like this:

(function() {

	var script = document.createElement( "script" );
	script.setAttribute( "type", "text/javascript" );

	// Augment the window object inside this Script tag body.
	script.textContent = ` = "bar";`;

	document.documentElement.appendChild( script );


As you can see, we're explicitly creating and injecting a <script> tag. And, if this content script were loaded into our parent page, we would then find that was defined as "bar".

For my Echo Log MVP, what I'm going to do is put my entire echo.js file content right into the content script. Then, I'm gonna have Chrome load my content script as the very first piece of content on the page. To do this, I'm going to use the run_at value of document_start, which is documented as:

Scripts are injected after any files from css, but before any other DOM is constructed or any other script is run.

This is one in the manifest.json file:

	"name": "Echo Log MVP",
	"description": "An enhancement for console.log() that allows for easy styling.",
	"version": "1.0",
	"manifest_version": 2,
	"browser_action": {
		"default_icon": "icon-128.png"
	"content_scripts": [
			"matches": [
			"js": [
			"run_at": "document_start"

If you look at the content_scripts entry, you'll see that I am matching against my local development URLs (which means that this Chrome extension won't activate anywhere else except for my local environment); and, I'm having Chrome inject the boostrap.js file as the very first piece of content.

Because of the limitations around our ability to modify the window object from within a Chrome extension, the bootstrap.js JavaScript file ends up being quite large (several hundred lines of code) because I have to inline my window object augmentation. The following file is basically an aggregation of the two files from my previous post:

// Inject script content at the top of the HTML document.
injectScriptContent( installEchoScriptContent );
injectScriptContent( installCustomEchoStylerContent );

// ----------------------------------------------------------------------------------- //
// ----------------------------------------------------------------------------------- //

// I inject and execute the given IIFE (immediately-invoked function expression) into the
// current HTML document.
function injectScriptContent( iifeFunction ) {

	var script = document.createElement( "script" );
	script.setAttribute( "type", "text/javascript" );
	script.setAttribute( "data-source", "Injected by Echo-Log Chrome Extension." );
	script.textContent = `;( ${ iifeFunction.toString() } )();`;

	document.documentElement.appendChild( script );


// I define custom echo stylers for the current page.
function installCustomEchoStylerContent() {

		// The list of colors taken from MDN
		// --
		.defineStyler( "black", "color: #000000" )
		.defineStyler( "bgBlack", "background-color: #000000" )
		.defineStyler( "silver", "color: #c0c0c0" )
		.defineStyler( "bgSilver", "background-color: #c0c0c0" )
		.defineStyler( "gray", "color: #808080" )
		.defineStyler( "bgGray", "background-color: #808080" )
		.defineStyler( "white", "color: #ffffff" )
		.defineStyler( "bgWhite", "background-color: #ffffff" )
		.defineStyler( "maroon", "color: #800000" )
		.defineStyler( "bgMaroon", "background-color: #800000" )
		.defineStyler( "red", "color: #ff0000" )
		.defineStyler( "bgRed", "background-color: #ff0000" )
		.defineStyler( "purple", "color: #800080" )
		.defineStyler( "bgPurple", "background-color: #800080" )
		.defineStyler( "fuchsia", "color: #ff00ff" )
		.defineStyler( "bgFuchsia", "background-color: #ff00ff" )
		.defineStyler( "green", "color: #008000" )
		.defineStyler( "bgGreen", "background-color: #008000" )
		.defineStyler( "lime", "color: #00ff00" )
		.defineStyler( "bgLime", "background-color: #00ff00" )
		.defineStyler( "olive", "color: #808000" )
		.defineStyler( "bgOlive", "background-color: #808000" )
		.defineStyler( "yellow", "color: #ffff00" )
		.defineStyler( "bgYellow", "background-color: #ffff00" )
		.defineStyler( "navy", "color: #000080" )
		.defineStyler( "bgNavy", "background-color: #000080" )
		.defineStyler( "blue", "color: #0000ff" )
		.defineStyler( "bgBlue", "background-color: #0000ff" )
		.defineStyler( "teal", "color: #008080" )
		.defineStyler( "bgTeal", "background-color: #008080" )
		.defineStyler( "aqua", "color: #00ffff" )
		.defineStyler( "bgAqua", "background-color: #00ffff" )
		.defineStyler( "orange", "color: #ffa500" )
		.defineStyler( "bgOrange", "background-color: #ffa500" )
		.defineStyler( "aliceblue", "color: #f0f8ff" )
		.defineStyler( "bgAliceblue", "background-color: #f0f8ff" )
		.defineStyler( "antiquewhite", "color: #faebd7" )
		.defineStyler( "bgAntiquewhite", "background-color: #faebd7" )
		.defineStyler( "aquamarine", "color: #7fffd4" )
		.defineStyler( "bgAquamarine", "background-color: #7fffd4" )
		.defineStyler( "azure", "color: #f0ffff" )
		.defineStyler( "bgAzure", "background-color: #f0ffff" )
		.defineStyler( "beige", "color: #f5f5dc" )
		.defineStyler( "bgBeige", "background-color: #f5f5dc" )
		.defineStyler( "bisque", "color: #ffe4c4" )
		.defineStyler( "bgBisque", "background-color: #ffe4c4" )
		.defineStyler( "blanchedalmond", "color: #ffebcd" )
		.defineStyler( "bgBlanchedalmond", "background-color: #ffebcd" )
		.defineStyler( "blueviolet", "color: #8a2be2" )
		.defineStyler( "bgBlueviolet", "background-color: #8a2be2" )
		.defineStyler( "brown", "color: #a52a2a" )
		.defineStyler( "bgBrown", "background-color: #a52a2a" )
		.defineStyler( "burlywood", "color: #deb887" )
		.defineStyler( "bgBurlywood", "background-color: #deb887" )
		.defineStyler( "cadetblue", "color: #5f9ea0" )
		.defineStyler( "bgCadetblue", "background-color: #5f9ea0" )
		.defineStyler( "chartreuse", "color: #7fff00" )
		.defineStyler( "bgChartreuse", "background-color: #7fff00" )
		.defineStyler( "chocolate", "color: #d2691e" )
		.defineStyler( "bgChocolate", "background-color: #d2691e" )
		.defineStyler( "coral", "color: #ff7f50" )
		.defineStyler( "bgCoral", "background-color: #ff7f50" )
		.defineStyler( "cornflowerblue", "color: #6495ed" )
		.defineStyler( "bgCornflowerblue", "background-color: #6495ed" )
		.defineStyler( "cornsilk", "color: #fff8dc" )
		.defineStyler( "bgCornsilk", "background-color: #fff8dc" )
		.defineStyler( "crimson", "color: #dc143c" )
		.defineStyler( "bgCrimson", "background-color: #dc143c" )
		.defineStyler( "cyan", "color: #00ffff" )
		.defineStyler( "bgCyan", "background-color: #00ffff" )
		.defineStyler( "darkblue", "color: #00008b" )
		.defineStyler( "bgDarkblue", "background-color: #00008b" )
		.defineStyler( "darkcyan", "color: #008b8b" )
		.defineStyler( "bgDarkcyan", "background-color: #008b8b" )
		.defineStyler( "darkgoldenrod", "color: #b8860b" )
		.defineStyler( "bgDarkgoldenrod", "background-color: #b8860b" )
		.defineStyler( "darkgray", "color: #a9a9a9" )
		.defineStyler( "bgDarkgray", "background-color: #a9a9a9" )
		.defineStyler( "darkgreen", "color: #006400" )
		.defineStyler( "bgDarkgreen", "background-color: #006400" )
		.defineStyler( "darkgrey", "color: #a9a9a9" )
		.defineStyler( "bgDarkgrey", "background-color: #a9a9a9" )
		.defineStyler( "darkkhaki", "color: #bdb76b" )
		.defineStyler( "bgDarkkhaki", "background-color: #bdb76b" )
		.defineStyler( "darkmagenta", "color: #8b008b" )
		.defineStyler( "bgDarkmagenta", "background-color: #8b008b" )
		.defineStyler( "darkolivegreen", "color: #556b2f" )
		.defineStyler( "bgDarkolivegreen", "background-color: #556b2f" )
		.defineStyler( "darkorange", "color: #ff8c00" )
		.defineStyler( "bgDarkorange", "background-color: #ff8c00" )
		.defineStyler( "darkorchid", "color: #9932cc" )
		.defineStyler( "bgDarkorchid", "background-color: #9932cc" )
		.defineStyler( "darkred", "color: #8b0000" )
		.defineStyler( "bgDarkred", "background-color: #8b0000" )
		.defineStyler( "darksalmon", "color: #e9967a" )
		.defineStyler( "bgDarksalmon", "background-color: #e9967a" )
		.defineStyler( "darkseagreen", "color: #8fbc8f" )
		.defineStyler( "bgDarkseagreen", "background-color: #8fbc8f" )
		.defineStyler( "darkslateblue", "color: #483d8b" )
		.defineStyler( "bgDarkslateblue", "background-color: #483d8b" )
		.defineStyler( "darkslategray", "color: #2f4f4f" )
		.defineStyler( "bgDarkslategray", "background-color: #2f4f4f" )
		.defineStyler( "darkslategrey", "color: #2f4f4f" )
		.defineStyler( "bgDarkslategrey", "background-color: #2f4f4f" )
		.defineStyler( "darkturquoise", "color: #00ced1" )
		.defineStyler( "bgDarkturquoise", "background-color: #00ced1" )
		.defineStyler( "darkviolet", "color: #9400d3" )
		.defineStyler( "bgDarkviolet", "background-color: #9400d3" )
		.defineStyler( "deeppink", "color: #ff1493" )
		.defineStyler( "bgDeeppink", "background-color: #ff1493" )
		.defineStyler( "deepskyblue", "color: #00bfff" )
		.defineStyler( "bgDeepskyblue", "background-color: #00bfff" )
		.defineStyler( "dimgray", "color: #696969" )
		.defineStyler( "bgDimgray", "background-color: #696969" )
		.defineStyler( "dimgrey", "color: #696969" )
		.defineStyler( "bgDimgrey", "background-color: #696969" )
		.defineStyler( "dodgerblue", "color: #1e90ff" )
		.defineStyler( "bgDodgerblue", "background-color: #1e90ff" )
		.defineStyler( "firebrick", "color: #b22222" )
		.defineStyler( "bgFirebrick", "background-color: #b22222" )
		.defineStyler( "floralwhite", "color: #fffaf0" )
		.defineStyler( "bgFloralwhite", "background-color: #fffaf0" )
		.defineStyler( "forestgreen", "color: #228b22" )
		.defineStyler( "bgForestgreen", "background-color: #228b22" )
		.defineStyler( "gainsboro", "color: #dcdcdc" )
		.defineStyler( "bgGainsboro", "background-color: #dcdcdc" )
		.defineStyler( "ghostwhite", "color: #f8f8ff" )
		.defineStyler( "bgGhostwhite", "background-color: #f8f8ff" )
		.defineStyler( "gold", "color: #ffd700" )
		.defineStyler( "bgGold", "background-color: #ffd700" )
		.defineStyler( "goldenrod", "color: #daa520" )
		.defineStyler( "bgGoldenrod", "background-color: #daa520" )
		.defineStyler( "greenyellow", "color: #adff2f" )
		.defineStyler( "bgGreenyellow", "background-color: #adff2f" )
		.defineStyler( "grey", "color: #808080" )
		.defineStyler( "bgGrey", "background-color: #808080" )
		.defineStyler( "honeydew", "color: #f0fff0" )
		.defineStyler( "bgHoneydew", "background-color: #f0fff0" )
		.defineStyler( "hotpink", "color: #ff69b4" )
		.defineStyler( "bgHotpink", "background-color: #ff69b4" )
		.defineStyler( "indianred", "color: #cd5c5c" )
		.defineStyler( "bgIndianred", "background-color: #cd5c5c" )
		.defineStyler( "indigo", "color: #4b0082" )
		.defineStyler( "bgIndigo", "background-color: #4b0082" )
		.defineStyler( "ivory", "color: #fffff0" )
		.defineStyler( "bgIvory", "background-color: #fffff0" )
		.defineStyler( "khaki", "color: #f0e68c" )
		.defineStyler( "bgKhaki", "background-color: #f0e68c" )
		.defineStyler( "lavender", "color: #e6e6fa" )
		.defineStyler( "bgLavender", "background-color: #e6e6fa" )
		.defineStyler( "lavenderblush", "color: #fff0f5" )
		.defineStyler( "bgLavenderblush", "background-color: #fff0f5" )
		.defineStyler( "lawngreen", "color: #7cfc00" )
		.defineStyler( "bgLawngreen", "background-color: #7cfc00" )
		.defineStyler( "lemonchiffon", "color: #fffacd" )
		.defineStyler( "bgLemonchiffon", "background-color: #fffacd" )
		.defineStyler( "lightblue", "color: #add8e6" )
		.defineStyler( "bgLightblue", "background-color: #add8e6" )
		.defineStyler( "lightcoral", "color: #f08080" )
		.defineStyler( "bgLightcoral", "background-color: #f08080" )
		.defineStyler( "lightcyan", "color: #e0ffff" )
		.defineStyler( "bgLightcyan", "background-color: #e0ffff" )
		.defineStyler( "lightgoldenrodyellow", "color: #fafad2" )
		.defineStyler( "bgLightgoldenrodyellow", "background-color: #fafad2" )
		.defineStyler( "lightgray", "color: #d3d3d3" )
		.defineStyler( "bgLightgray", "background-color: #d3d3d3" )
		.defineStyler( "lightgreen", "color: #90ee90" )
		.defineStyler( "bgLightgreen", "background-color: #90ee90" )
		.defineStyler( "lightgrey", "color: #d3d3d3" )
		.defineStyler( "bgLightgrey", "background-color: #d3d3d3" )
		.defineStyler( "lightpink", "color: #ffb6c1" )
		.defineStyler( "bgLightpink", "background-color: #ffb6c1" )
		.defineStyler( "lightsalmon", "color: #ffa07a" )
		.defineStyler( "bgLightsalmon", "background-color: #ffa07a" )
		.defineStyler( "lightseagreen", "color: #20b2aa" )
		.defineStyler( "bgLightseagreen", "background-color: #20b2aa" )
		.defineStyler( "lightskyblue", "color: #87cefa" )
		.defineStyler( "bgLightskyblue", "background-color: #87cefa" )
		.defineStyler( "lightslategray", "color: #778899" )
		.defineStyler( "bgLightslategray", "background-color: #778899" )
		.defineStyler( "lightslategrey", "color: #778899" )
		.defineStyler( "bgLightslategrey", "background-color: #778899" )
		.defineStyler( "lightsteelblue", "color: #b0c4de" )
		.defineStyler( "bgLightsteelblue", "background-color: #b0c4de" )
		.defineStyler( "lightyellow", "color: #ffffe0" )
		.defineStyler( "bgLightyellow", "background-color: #ffffe0" )
		.defineStyler( "limegreen", "color: #32cd32" )
		.defineStyler( "bgLimegreen", "background-color: #32cd32" )
		.defineStyler( "linen", "color: #faf0e6" )
		.defineStyler( "bgLinen", "background-color: #faf0e6" )
		.defineStyler( "magenta", "color: #ff00ff" )
		.defineStyler( "bgMagenta", "background-color: #ff00ff" )
		.defineStyler( "mediumaquamarine", "color: #66cdaa" )
		.defineStyler( "bgMediumaquamarine", "background-color: #66cdaa" )
		.defineStyler( "mediumblue", "color: #0000cd" )
		.defineStyler( "bgMediumblue", "background-color: #0000cd" )
		.defineStyler( "mediumorchid", "color: #ba55d3" )
		.defineStyler( "bgMediumorchid", "background-color: #ba55d3" )
		.defineStyler( "mediumpurple", "color: #9370db" )
		.defineStyler( "bgMediumpurple", "background-color: #9370db" )
		.defineStyler( "mediumseagreen", "color: #3cb371" )
		.defineStyler( "bgMediumseagreen", "background-color: #3cb371" )
		.defineStyler( "mediumslateblue", "color: #7b68ee" )
		.defineStyler( "bgMediumslateblue", "background-color: #7b68ee" )
		.defineStyler( "mediumspringgreen", "color: #00fa9a" )
		.defineStyler( "bgMediumspringgreen", "background-color: #00fa9a" )
		.defineStyler( "mediumturquoise", "color: #48d1cc" )
		.defineStyler( "bgMediumturquoise", "background-color: #48d1cc" )
		.defineStyler( "mediumvioletred", "color: #c71585" )
		.defineStyler( "bgMediumvioletred", "background-color: #c71585" )
		.defineStyler( "midnightblue", "color: #191970" )
		.defineStyler( "bgMidnightblue", "background-color: #191970" )
		.defineStyler( "mintcream", "color: #f5fffa" )
		.defineStyler( "bgMintcream", "background-color: #f5fffa" )
		.defineStyler( "mistyrose", "color: #ffe4e1" )
		.defineStyler( "bgMistyrose", "background-color: #ffe4e1" )
		.defineStyler( "moccasin", "color: #ffe4b5" )
		.defineStyler( "bgMoccasin", "background-color: #ffe4b5" )
		.defineStyler( "navajowhite", "color: #ffdead" )
		.defineStyler( "bgNavajowhite", "background-color: #ffdead" )
		.defineStyler( "oldlace", "color: #fdf5e6" )
		.defineStyler( "bgOldlace", "background-color: #fdf5e6" )
		.defineStyler( "olivedrab", "color: #6b8e23" )
		.defineStyler( "bgOlivedrab", "background-color: #6b8e23" )
		.defineStyler( "orangered", "color: #ff4500" )
		.defineStyler( "bgOrangered", "background-color: #ff4500" )
		.defineStyler( "orchid", "color: #da70d6" )
		.defineStyler( "bgOrchid", "background-color: #da70d6" )
		.defineStyler( "palegoldenrod", "color: #eee8aa" )
		.defineStyler( "bgPalegoldenrod", "background-color: #eee8aa" )
		.defineStyler( "palegreen", "color: #98fb98" )
		.defineStyler( "bgPalegreen", "background-color: #98fb98" )
		.defineStyler( "paleturquoise", "color: #afeeee" )
		.defineStyler( "bgPaleturquoise", "background-color: #afeeee" )
		.defineStyler( "palevioletred", "color: #db7093" )
		.defineStyler( "bgPalevioletred", "background-color: #db7093" )
		.defineStyler( "papayawhip", "color: #ffefd5" )
		.defineStyler( "bgPapayawhip", "background-color: #ffefd5" )
		.defineStyler( "peachpuff", "color: #ffdab9" )
		.defineStyler( "bgPeachpuff", "background-color: #ffdab9" )
		.defineStyler( "peru", "color: #cd853f" )
		.defineStyler( "bgPeru", "background-color: #cd853f" )
		.defineStyler( "pink", "color: #ffc0cb" )
		.defineStyler( "bgPink", "background-color: #ffc0cb" )
		.defineStyler( "plum", "color: #dda0dd" )
		.defineStyler( "bgPlum", "background-color: #dda0dd" )
		.defineStyler( "powderblue", "color: #b0e0e6" )
		.defineStyler( "bgPowderblue", "background-color: #b0e0e6" )
		.defineStyler( "rosybrown", "color: #bc8f8f" )
		.defineStyler( "bgRosybrown", "background-color: #bc8f8f" )
		.defineStyler( "royalblue", "color: #4169e1" )
		.defineStyler( "bgRoyalblue", "background-color: #4169e1" )
		.defineStyler( "saddlebrown", "color: #8b4513" )
		.defineStyler( "bgSaddlebrown", "background-color: #8b4513" )
		.defineStyler( "salmon", "color: #fa8072" )
		.defineStyler( "bgSalmon", "background-color: #fa8072" )
		.defineStyler( "sandybrown", "color: #f4a460" )
		.defineStyler( "bgSandybrown", "background-color: #f4a460" )
		.defineStyler( "seagreen", "color: #2e8b57" )
		.defineStyler( "bgSeagreen", "background-color: #2e8b57" )
		.defineStyler( "seashell", "color: #fff5ee" )
		.defineStyler( "bgSeashell", "background-color: #fff5ee" )
		.defineStyler( "sienna", "color: #a0522d" )
		.defineStyler( "bgSienna", "background-color: #a0522d" )
		.defineStyler( "skyblue", "color: #87ceeb" )
		.defineStyler( "bgSkyblue", "background-color: #87ceeb" )
		.defineStyler( "slateblue", "color: #6a5acd" )
		.defineStyler( "bgSlateblue", "background-color: #6a5acd" )
		.defineStyler( "slategray", "color: #708090" )
		.defineStyler( "bgSlategray", "background-color: #708090" )
		.defineStyler( "slategrey", "color: #708090" )
		.defineStyler( "bgSlategrey", "background-color: #708090" )
		.defineStyler( "snow", "color: #fffafa" )
		.defineStyler( "bgSnow", "background-color: #fffafa" )
		.defineStyler( "springgreen", "color: #00ff7f" )
		.defineStyler( "bgSpringgreen", "background-color: #00ff7f" )
		.defineStyler( "steelblue", "color: #4682b4" )
		.defineStyler( "bgSteelblue", "background-color: #4682b4" )
		.defineStyler( "tan", "color: #d2b48c" )
		.defineStyler( "bgTan", "background-color: #d2b48c" )
		.defineStyler( "thistle", "color: #d8bfd8" )
		.defineStyler( "bgThistle", "background-color: #d8bfd8" )
		.defineStyler( "tomato", "color: #ff6347" )
		.defineStyler( "bgTomato", "background-color: #ff6347" )
		.defineStyler( "turquoise", "color: #40e0d0" )
		.defineStyler( "bgTurquoise", "background-color: #40e0d0" )
		.defineStyler( "violet", "color: #ee82ee" )
		.defineStyler( "bgViolet", "background-color: #ee82ee" )
		.defineStyler( "wheat", "color: #f5deb3" )
		.defineStyler( "bgWheat", "background-color: #f5deb3" )
		.defineStyler( "whitesmoke", "color: #f5f5f5" )
		.defineStyler( "bgWhitesmoke", "background-color: #f5f5f5" )
		.defineStyler( "yellowgreen", "color: #9acd32" )
		.defineStyler( "bgYellowgreen", "background-color: #9acd32" )
		.defineStyler( "rebeccapurple", "color: #663399" )
		.defineStyler( "bgRebeccapurple", "background-color: #663399" )

		// Custom stylers I use in my code.
		.defineStyler( "monospace", "font-family: monospace" )
		.defineStyler( "linethrough", echo.strikethrough )
		.defineStyler( "asTag", echo.rounded.padded.monospace )
		.defineStyler( "asAlert", echo.asTag.bgRed.white.bold )
		.defineStyler( "asWarning", )


// I define the echo() API for outputting styles log statements.
// --
// NOTE: This is more-or-less a direct copy from the script located here:
function installEchoScriptContent() {

	var stylers = {
		// NOTE: All TEXT COLOR and BACKGROUND COLOR stylers have been moved into the
		// custom echo stylers above. There was no need to define them more than once.
		// --
		// Text modifiers.
		bold: "font-weight: bold",
		lighter: "font-weight: lighter",
		italic: "font-style: italic",
		strikethrough: "text-decoration: line-through",
		underline: "text-decoration: underline",
		large: "font-size: 16px",
		larger: "font-size: 22px",
		largest: "font-size: 26px",
		massive: "font-size: 36px",

		// Block modifiers.
		padded: "display: inline-block ; padding: 4px 6px",
		rounded: "display: inline-block ; border-radius: 4px"

	var rootStyler = "";

	// As "styler" functions are called, they are going to push values and CSS onto this
	// queue. Then, when the "log" functions are called, this queue will be processed and
	// cleared (for the next set of styler invocations).
	var logItemQueue = [];

	// When the "styler" functions are called, they populate the queue (above). As such,
	// their return value isn't directly consumable. Therefore, they return this token
	// which helps our queue-processor differentiate from a styler value vs. a raw value.
	// And, the embedded warning helps the developer understand where / if they made a
	// mistake in how the styler return value was used.
	var ECHO_TOKEN = {
		warning: "This value should not be used directly - it should be an argument to an echo invocation."
	var RESET_INPUT = "%c ";
	var RESET_CSS = "";

	var coreApi = {
		log: wrapConsoleFunction( console.log ),
		warn: wrapConsoleFunction( console.warn ),
		error: wrapConsoleFunction( console.error ),
		trace: wrapConsoleFunction( console.trace ),
		group: wrapConsoleFunction( ),
		groupEnd: wrapConsoleFunction( console.groupEnd ),
		defineStyler: defineStyler,
		defineRootStyler: defineRootStyler

	// We want all of our "stylers" to hang off the core API. And, since the collection
	// of stylers can change over time (using aliases and customizations), we have to
	// proxy the core API such that we can dynamically see if a styler is being accessed.
	var coreApiProxy = new Proxy(
			get: function( target, prop, receiver ) {

				// Intercept styler access.
				if ( prop in stylers ) {

					return( createStylerProxy( prop ) );


				return( target[ prop ] );


	return( window.echo = coreApiProxy );

	// ---
	// ---

	// I define the root CSS that all other styles will start with.
	// --
	// NOTE: This method should be called before any other stylers are created.
	function defineRootStyler( rawCSS ) {

		rootStyler = rawCSS;
		return( this );


	// I allow new stylers to be defined. The "newStyler" can be a string of raw CSS; or,
	// it can be a reference to another styler.
	function defineStyler( name, newStyler ) {

		if ( typeof( newStyler ) === "string" ) {

			stylers[ name ] = newStyler;
			return( this );

		} else {

			stylers[ name ] = newStyler.proxyCSS;
			return( this );



	// ---
	// ---

	// Every "styler" needs to hang off of very other styler. And, as each styler is
	// accessed, it needs to aggregate the pending CSS from all of the previous stylers
	// in the access path. To do this, we're going to use a Proxy object.
	function createStylerProxy( rootProp, rootCSS = "" ) {

		var proxyCSS = ( rootCSS + ";" + stylers[ rootProp ] );

		// Every "styler" ultimately needs to be a Function call that applies the
		// aggregate CSS to the given value.
		var applyAggregateCSS = function( value ) {

				value: value,
				css: ( rootStyler + ";" + proxyCSS )

			return( ECHO_TOKEN );


		var stylerProxy = new Proxy(
				get: function( target, prop ) {

					// Since we can alias styler proxies, we need a way to return the
					// aggregated CSS for any given proxy.
					if ( prop === "proxyCSS" ) {

						return( proxyCSS );


					if ( prop in stylers ) {

						return( createStylerProxy( prop, proxyCSS ) );



		return( stylerProxy );


	// I provide an echo-based wrapper for the given Console Function. This uses an
	// internal queue to aggregate values before calling the underlying Console Function
	// with the desired CSS formatting.
	function wrapConsoleFunction( consoleFunction ) {

		function consoleFunctionWrapper() {

			// As we loop over the arguments, we're going to aggregate a set of inputs
			// and modifiers. The Inputs will ultimately be collapsed down into a single
			// string that acts as the first console.log parameter while the modifiers
			// are then SPREAD into console.log as 2...N.
			// --
			// NOTE: After each input/modifier pair, I'm adding a RESET pairing. This
			// implicitly resets the CSS after every formatted pairing.
			var inputs = [];
			var modifiers = [];

			for ( var rawArg of arguments ) {

				// When the styler methods are called, they return a special token. This
				// token indicates that we should pull the corresponding value out of the
				// QUEUE instead of trying to consume the given argument directly.
				if ( rawArg === ECHO_TOKEN ) {

					var item = logItemQueue.shift();

					inputs.push( ( "%c" + item.value ), RESET_INPUT );
					modifiers.push( item.css, RESET_CSS );

				// For every other argument type, output the value directly.
				} else {

					if (
						( typeof( rawArg ) === "object" ) ||
						( typeof( rawArg ) === "function" )
						) {

						inputs.push( "%o", RESET_INPUT );
						modifiers.push( rawArg, RESET_CSS );

					} else {

						inputs.push( ( "%c" + rawArg ), RESET_INPUT );
						modifiers.push( RESET_CSS, RESET_CSS );




			consoleFunction( inputs.join( "" ), ...modifiers );

			// Once we output the aggregated value, reset the queue. This should have
			// already been emptied by the .shift() calls; but the explicit reset here
			// acts as both a marker of intention as well as a fail-safe.
			logItemQueue = [];


		return( consoleFunctionWrapper );



Now, with this Echo-Log Chrome browser extension installed, if I visit my local application - or the Chrome Developer site (the other set of URLs that I was matching against) - we can see that my two <script> tags show up at the very top of the HTML page:

Echo-log Chrome extension content script is injected as the first script in the HTML page.

And, because the programmatically injected <script> tag is executing in the context of the embedding page, it can successfully modify the window object. Which means, if we then open the Chrome Developer Tools, we'll see that our echo object is ready to be used at any point during execution:

An echo.log() statement being executed after the content script has been loaded.

Now, having these JavaScript and JSON files on your computer doesn't magically make Chrome run them - they have to be loaded into Chrome as an extension. For this MVP, instead of trying to publish this anywhere, which wouldn't make sense given my local-development URL targeting, I'm loading them in as an "unpacked extension":

Loading the Echo-Log extension as an unpacked extension in the Chrome extensions module.

This allows me to use the local file system as the source of my Chrome extension. Now, I can go in an edit the files and all I have to do is hit the little reload-button and kablamo: Chrome is running my latest updates.

Chrome browser extensions seem really cool! I hope I didn't say anything overtly wrong in this post - this was pieced together based on the intro on the Chrome Developers Site and some StackOverflow posts. But now, MVP-style, I can console-log like a boss!

Want to use code from this post? Check out the license.

Reader Comments

I believe in love. I believe in compassion. I believe in human rights. I believe that we can afford to give more of these gifts to the world around us because it costs us nothing to be decent and kind and understanding. And, I want you to know that when you land on this site, you are accepted for who you are, no matter how you identify, what truths you live, or whatever kind of goofy shit makes you feel alive! Rock on with your bad self!
Ben Nadel