TypeScript - pad left number in string with zeros or spaces to get determined length

In TypeScript, it is possible to pad left a number with any character in the following ways.

1. Custom solution example

const padLeft = (number: number, length: number, character: string = '0'): string => {
  let result = String(number);
  for (let i = result.length; i < length; ++i) {
    result = character + result;
  }
  return result;
};


// Usage example:

console.log(padLeft(123, 2)); // 123
console.log(padLeft(123, 4)); // 0123
console.log(padLeft(123, 6)); // 000123
console.log(padLeft(123, 6, '*')); // ***123
console.log(padLeft(123, 6, ' ')); //    123

2. Polifill example

ECMAScript 2017 introduced a function that pads numbers.

Simple steps:

1. install ts-polyfill package:

npm install ts-polyfill

2. inside tsconfig.json add es2017.string to the lib.

{
    "version" : "3.0.3",
    "compilerOptions" : {
        "target": "ES6",
        //...
        "lib": ["es2017.string", /*...*/]
        //...
    },
    "include": [
        "./**/*.ts"
    ]
}

3. Run the example

The example below was executed under Node.js:

// https://github.com/ryanelian/ts-polyfill
// https://developer.mozilla.org/en-US/docs/Web/TypeScript/Reference/Global_Objects/String/padStart

import 'ts-polyfill/lib/es2017-string';

const text = '123';

console.log(text.padStart(2));
console.log(text.padStart(4));
console.log(text.padStart(6));
console.log(text.padStart(6, '0'));
console.log(text.padStart(6, '*'));

Warning: under Node.js do not forget to add console.log() declarations.

Output:

123
 123
   123
000123
***123

See also

1. TypeScript - pad right number in string with zeros or spaces to get determined length