add comma to number

Question

Given a number, please create a function to add commas as thousand separators.

addComma(1) // '1'
addComma(1000) // '1,000'
addComma(-12345678) // '-12,345,678'
addComma(12345678.12345) // '12,345,678.12345'

Input are all valid numbers.

Code

/**
 * @param {number} num
 * @return {string}
 */
function addComma(num) {
  // your code here
}

Source

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