create a sum()

Question

Create a sum(), which makes following possible

const sum1 = sum(1)
sum1(2) == 3 // true
sum1(3) == 4 // true
sum(1)(2)(3) == 6 // true
sum(5)(-1)(2) == 6 // true

Code

/**
 * @param {number} num
 */
function sum(num) {
  // your code here
}

Source

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