inject code into script tags based on a search string

inject.js

// helper used to inject code into script tags based on a search string
var inject = function (searchString, codeToInject) {
	// find the relevant script tag
	var scriptTags = document.getElementsByTagName('script');
	var scriptTag;
	var code;
	for (var i = 0; i < scriptTags.length; ++i) {
		scriptTag = scriptTags[i];
		if (
			scriptTag.textContent.indexOf(searchString) >= 0 // script contains the search string
			&&
			scriptTag != document.currentScript // script isn't the one doing the injecting (which also contains the search string)
		) {
			code = scriptTag.textContent;
			break;
		}
	}

	// error-handling
	if (!code) {
		throw 'Couldn\'t find "' + searchString + '" in script tags';
	}

	// modify the content
	code = code.replace(searchString, searchString + codeToInject);

	// replace the old script tag with a new one using our modified code
	scriptTag.remove();
	scriptTag = document.createElement('script');
	scriptTag.textContent = code;
	document.head.appendChild(scriptTag);
};