How Can I Pad Numbers with Leading Zeros in JavaScript?

Padding Numbers with Leading Zeros in JavaScript

Original Question:

Can JavaScript be used to pad a number with leading zeros to a specified width? For example, a number like 9 should be padded to "0009" with three leading zeros.

Solution:

ES2017 Update:

• String.prototype.padStart(): This built-in method allows padding a string with a specified number of characters at the beginning:

  n = 9;
  String(n).padStart(4, '0'); // '0009'

Legacy Approach:

• Custom Function: If ES2017 features are not available, a custom function can be created to pad the number:

  function pad(n, width, z) {
  z = z || '0';
  n = n + '';
  return n.length >= width ? n : new Array(width - n.length + 1).join(z) + n;
  }

• This function takes three parameters: the number to pad (n), the desired width (width), and an optional padding character (z, defaults to '0').
• It converts the number to a string and checks its length against the desired width.
• If the number is shorter than the desired width, the function creates an array with the required number of elements, filled with the padding character.
• The array elements are joined into a string and prepended to the number to achieve the desired padding.

Example Usage:

pad(10, 4);      // 0010
pad(9, 4);       // 0009
pad(123, 4);     // 0123

pad(10, 4, '-'); // --10

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