String.prototype.split()

separator

The pattern describing where each split should occur. Can be undefined, a string, or an object with a Symbol.split method — the typical example being a regular expression. Omitting separator or passing undefined causes split() to return an array with the calling string as a single element. All values that are not undefined or objects with a [Symbol.split]() method are coerced to strings.

limit Optional

A non-negative integer specifying a limit on the number of substrings to be included in the array. If provided, splits the string at each occurrence of the specified separator, but stops when limit entries have been placed in the array. Any leftover text is not included in the array at all.

• The array may contain fewer entries than limit if the end of the string is reached before the limit is reached.
• If limit is 0, [] is returned.

An Array of strings, split at each point where the separator occurs in the given string.

If separator is a non-empty string, the target string is split by all matches of the separator without including separator in the results. For example, a string containing tab separated values (TSV) could be parsed by passing a tab character as the separator, like myString.split("\t"). If separator contains multiple characters, that entire character sequence must be found in order to split. If separator appears at the beginning (or end) of the string, it still has the effect of splitting, resulting in an empty (i.e. zero length) string appearing at the first (or last) position of the returned array. If separator does not occur in str, the returned array contains one element consisting of the entire string.

If separator is an empty string (""), str is converted to an array of each of its UTF-16 "characters", without empty strings on either ends of the resulting string.

If separator is a regexp that matches empty strings, whether the match is split by UTF-16 code units or Unicode code points depends on if the regex is Unicode-aware.

"😄😄".split(/(?:)/); // [ "\ud83d", "\ude04", "\ud83d", "\ude04" ]
"😄😄".split(/(?:)/u); // [ "😄", "😄" ]

If separator is a regular expression with capturing groups, then each time separator matches, the captured groups (including any undefined results) are spliced into the output array. This behavior is specified by the regexp's Symbol.split method.

If separator is an object with a Symbol.split method, that method is called with the target string and limit as arguments, and this set to the object. Its return value becomes the return value of split.

Any other value will be coerced to a string before being used as separator.

When the string is empty and a non-empty separator is specified, split() returns [""]. If the string and separator are both empty strings, an empty array is returned.

const emptyString = "";

// string is empty and separator is non-empty
console.log(emptyString.split("a"));
// [""]

// string and separator are both empty strings
console.log(emptyString.split(emptyString));
// []

The following example defines a function that splits a string into an array of strings using separator. After splitting the string, the function logs messages indicating the original string (before the split), the separator used, the number of elements in the array, and the individual array elements.

function splitString(stringToSplit, separator) {
  const arrayOfStrings = stringToSplit.split(separator);

  console.log("The original string is:", stringToSplit);
  console.log("The separator is:", separator);
  console.log(
    "The array has",
    arrayOfStrings.length,
    "elements:",
    arrayOfStrings.join(" / "),
  );
}

const tempestString = "Oh brave new world that has such people in it.";
const monthString = "Jan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec";

const space = " ";
const comma = ",";

splitString(tempestString, space);
splitString(tempestString);
splitString(monthString, comma);

This example produces the following output:

The original string is: "Oh brave new world that has such people in it."
The separator is: " "
The array has 10 elements: Oh / brave / new / world / that / has / such / people / in / it.

The original string is: "Oh brave new world that has such people in it."
The separator is: "undefined"
The array has 1 elements: Oh brave new world that has such people in it.

The original string is: "Jan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec"
The separator is: ","
The array has 12 elements: Jan / Feb / Mar / Apr / May / Jun / Jul / Aug / Sep / Oct / Nov / Dec

In the following example, split() looks for zero or more spaces, followed by a semicolon, followed by zero or more spaces—and, when found, removes the spaces and the semicolon from the string. nameList is the array returned as a result of split().

const names = "Harry Trump ;Fred Barney; Helen Rigby ; Bill Abel ;Chris Hand ";

console.log(names);

const re = /\s*(?:;|$)\s*/;
const nameList = names.split(re);

console.log(nameList);

This logs two lines; the first line logs the original string, and the second line logs the resulting array.

Harry Trump ;Fred Barney; Helen Rigby ; Bill Abel ;Chris Hand
[ "Harry Trump", "Fred Barney", "Helen Rigby", "Bill Abel", "Chris Hand", "" ]

In the following example, split() looks for spaces in a string and returns the first 3 splits that it finds.

const myString = "Hello World. How are you doing?";
const splits = myString.split(" ", 3);

console.log(splits); // [ "Hello", "World.", "How" ]

If separator is a regular expression that contains capturing parentheses ( ), matched results are included in the array.

const myString = "Hello 1 word. Sentence number 2.";
const splits = myString.split(/(\d)/);

console.log(splits);
// [ "Hello ", "1", " word. Sentence number ", "2", "." ]

An object with a Symbol.split method can be used as a splitter with custom behavior.

The following example splits a string using an internal state consisting of an incrementing number:

const splitByNumber = {
  [Symbol.split](str) {
    let num = 1;
    let pos = 0;
    const result = [];
    while (pos < str.length) {
      const matchPos = str.indexOf(num, pos);
      if (matchPos === -1) {
        result.push(str.substring(pos));
        break;
      }
      result.push(str.substring(pos, matchPos));
      pos = matchPos + String(num).length;
      num++;
    }
    return result;
  },
};

const myString = "a1bc2c5d3e4f";
console.log(myString.split(splitByNumber)); // [ "a", "bc", "c5d", "e", "f" ]

The following example uses an internal state to enforce certain behavior, and to ensure a "valid" result is produced.

const DELIMITER = ";";

// Split the commands, but remove any invalid or unnecessary values.
const splitCommands = {
  [Symbol.split](str, lim) {
    const results = [];
    const state = {
      on: false,
      brightness: {
        current: 2,
        min: 1,
        max: 3,
      },
    };
    let pos = 0;
    let matchPos = str.indexOf(DELIMITER, pos);

    while (matchPos !== -1) {
      const subString = str.slice(pos, matchPos).trim();

      switch (subString) {
        case "light on":
          // If the `on` state is already true, do nothing.
          if (!state.on) {
            state.on = true;
            results.push(subString);
          }
          break;

        case "light off":
          // If the `on` state is already false, do nothing.
          if (state.on) {
            state.on = false;
            results.push(subString);
          }
          break;

        case "brightness up":
          // Enforce a brightness maximum.
          if (state.brightness.current < state.brightness.max) {
            state.brightness.current += 1;
            results.push(subString);
          }
          break;

        case "brightness down":
          // Enforce a brightness minimum.
          if (state.brightness.current > state.brightness.min) {
            state.brightness.current -= 1;
            results.push(subString);
          }
          break;
      }

      if (results.length === lim) {
        break;
      }

      pos = matchPos + DELIMITER.length;
      matchPos = str.indexOf(DELIMITER, pos);
    }

    // If we broke early due to reaching the split `lim`, don't add the remaining commands.
    if (results.length < lim) {
      results.push(str.slice(pos).trim());
    }

    return results;
  },
};

const commands =
  "light on; brightness up; brightness up; brightness up; light on; brightness down; brightness down; light off";
console.log(commands.split(splitCommands, 3)); // ["light on", "brightness up", "brightness down"]

• Polyfill of String.prototype.split in core-js with fixes and implementation of modern behavior like Symbol.split support
• String.prototype.charAt()
• String.prototype.indexOf()
• String.prototype.lastIndexOf()
• Array.prototype.join()
• Regular expressions guide