Avoid dynamically injecting the same script multiple times when using chrome.tabs.executeScript(…)

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It is absolutely a legitimate concern.

The easy way would be to use a mechanism similar to #ifndef include guards in C.

Define a flag that gets set once the content script gets executed, and check if it’s defined before doing anything. All scripts injected from the same extension share the JS execution context and therefore global scope.

Your content script might look like this:

if (window.contentScriptInjected !== true) {
    window.contentScriptInjected = true; // global scope

    /* Do your initialization and work */
}

/* global function definitions */

The check should use an explicit true value to avoid false positives on pages that happen to have an element with id attribute that accidentally equals the variable name – browsers create an implicit global variable that points to that DOM element so for an if check it’ll be truthy.

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