/this-vs-that GitHub 1316★

encodeURI vs encodeURIComponent

Because a URL can consist of standard ASCII characters only, other special characters have to be encoded. They will be replaced by a sequence of different characters that represent its UTF-8 encoding.

encodeURI and encodeURIComponent are used for that purpose.


  1. encodeURI is used to encode a full URL.

    encodeURI('https://domain.com/path to a document.pdf');

    // 'https://domain.com/path%20to%20a%20document.pdf'

    Whereas encodeURIComponent is used for encoding a URI component such as a query string.

    `http://domain.com/?search=\${encodeURIComponent('encode & decode param')}`;

    // 'http://domain.com/?search=encode%20%26%20decode%20param'
  2. There are 11 characters which are not encoded by encodeURI, but encoded by encodeURIComponent.

    The following snippet prints these characters:

    const arr = Array(256)
    .map((_, i) => String.fromCharCode(i))
    .filter((c) => encodeURI(c) != encodeURIComponent(c));

    arr.forEach((c) => console.log(c, encodeURI(c), encodeURIComponent(c)));

    Here is the list of those characters:


Good to know

  1. decodeURI and decodeURIComponent are methods to decode a string that is encoded by encodeURI and encodeURIComponent respectively.

  2. encodeURIComponent does not encode -_.!~*'(). If you want to these characters are encoded, you have to replace them with corresponding UTF-8 sequence of characters:

    const encode = (str) =>
    .replace(/\-/g, '%2D')
    .replace(/\_/g, '%5F')
    .replace(/\./g, '%2E')
    .replace(/\!/g, '%21')
    .replace(/\~/g, '%7E')
    .replace(/\*/g, '%2A')
    .replace(/\'/g, '%27')
    .replace(/\(/g, '%28')
    .replace(/\)/g, '%29');

    encode("What's result of (4 + 2)?"); // "What%27s%20result%20of%20%284%20%2B%202%29%3F"

    The decoding function could look like as follow:

    const decode = (str) =>
    .replace(/\\%2D/g, '-')
    .replace(/\\%5F/g, '_')
    .replace(/\\%2E/g, '.')
    .replace(/\\%21/g, '!')
    .replace(/\\%7E/g, '~')
    .replace(/\\%2A/g, '*')
    .replace(/\\%27/g, "'")
    .replace(/\\%28/g, '(')
    .replace(/\\%29/g, ')')

    decode('What%27s%20result%20of%20%284%20%2B%202%29%3F'); // "What's result of (4 + 2)?"
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