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    The substr() method returns the characters in a string beginning at the specified location through the specified number of characters.


    str.substr(start[, length])


    Location at which to begin extracting characters.
    The number of characters to extract.


    start is a character index. The index of the first character is 0, and the index of the last character is 1 less than the length of the string. substr begins extracting characters at start and collects length characters (unless it reaches the end of the string first, in which case it will return fewer).

    If start is positive and is greater than or equal to the length of the string, substr returns an empty string.

    If start is negative, substr uses it as a character index from the end of the string. If start is negative and abs(start) is larger than the length of the string, substr uses 0 as the start index. Note: the described handling of negative values of the start argument is not supported by Microsoft JScript .

    If length is 0 or negative, substr returns an empty string. If length is omitted, substr extracts characters to the end of the string.


    Example: Using substr

    var str = "abcdefghij";
    console.log("(1,2): "    + str.substr(1,2));   // (1,2): bc
    console.log("(-3,2): "   + str.substr(-3,2));  // (-3,2): hi
    console.log("(-3): "     + str.substr(-3));    // (-3): hij
    console.log("(1): "      + str.substr(1));     // (1): bcdefghij
    console.log("(-20, 2): " + str.substr(-20,2)); // (-20, 2): ab
    console.log("(20, 2): "  + str.substr(20,2));  // (20, 2):


    Microsoft's JScript does not support negative values for the start index. If you wish to make use of this feature, you can use the following compatibilty code to work around this bug:

    // only run when the substr function is broken
    if ('ab'.substr(-1) != 'b')
       *  Get the substring of a string
       *  @param  {integer}  start   where to start the substring
       *  @param  {integer}  length  how many characters to return
       *  @return {string}
      String.prototype.substr = function(substr) {
        return function(start, length) {
          // did we get a negative start, calculate how much it is
          // from the beginning of the string
          if (start < 0) start = this.length + start;
          // call the original function
          return, start, length);


    Specification Status Comment
    ECMAScript 3rd Edition. Standard Defined in the (informative) Compatibility Annex B.
    Implemented in JavaScript 1.0
    ECMAScript Language Specification 5.1th Edition (ECMA-262) Standard Defined in the (informative) Compatibility Annex B
    ECMAScript Language Specification 6th Edition (ECMA-262) Draft Defined in the (normative) Annex B for Additional ECMAScript Features for Web Browsers

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

    Note: Up to version 3.6, Firefox had a bug which caused substr to return empty result when an explicit undefined value was passed in as the length.

    See also

    Document Tags and Contributors

    Contributors to this page: Sheppy
    Last updated by: Sheppy,
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