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Cannot read property 'style' of undefined — Uncaught Type Error

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没有蜡笔的小新
没有蜡笔的小新 2021-02-13 14:49

I would like to change the color, fontsize and font weight of the text in a span element of the html page.

I am using the following code:

if(window.locat
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  • 既然无缘
    2021-02-13 15:29

    It's currently working, I've just changed the operator > in order to work in the snippet, take a look:

    window.onload = function() {

  if (window.location.href.indexOf("test") <= -1) {
    var search_span = document.getElementsByClassName("securitySearchQuery");
    search_span[0].style.color = "blue";
    search_span[0].style.fontWeight = "bold";
    search_span[0].style.fontSize = "40px";

  }

}
    <h1 class="keyword-title">Search results for<span class="securitySearchQuery"> "hi".</span></h1>

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  • 孤独总比滥情好
    2021-02-13 15:37

    Add your <script> to the bottom of your <body>, or add an event listener for DOMContentLoaded following this StackOverflow question.

    If that script executes in the <head> section of the code, document.getElementsByClassName(...) will return an empty array because the DOM is not loaded yet.

    You're getting the Type Error because you're referencing search_span[0], but search_span[0] is undefined.

    This works when you execute it in Dev Tools because the DOM is already loaded.

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