JavaScript Reference
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Quick Reference

The Element querySelector() method returns the first child element that matches the specified CSS selector or selectors of an element.

<div id="my_div">
    <p id="my_output">My content</p>
</div>
// variable
let my_query = document.getElementById('my_div');

// change the HTML element
my_query.querySelector('#my_output').innerHTML = 'Hello World';

Output

Hello World

Syntax

element.querySelector(CSS selectors separated by commas)

JavaScript Notes:

  • When using JavaScript, single or double quotation marks are acceptable and work identically to one another; choose whichever you prefer, and stay consistent
  • JavaScript is a case-sensitive language; firstName is NOT the same as firstname
  • Arrays count starting from zero NOT one; so item 1 is position [0], item 2 is position [1], and item 3 is position [2] … and so on
  • JavaScript variables must begin with a letter, $, or _
  • JavaScript variables are case sensitive (x is not the same as X)
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