Why is it important to understand the meaning of variable = [...variable] in Javascript ES6?

Question

Why is it important to understand the meaning of variable = [...variable] in Javascript ES6?

I need clarification on the following variable arg assignment

arg = [...arg];

Can you explain what this code snippet does?

javascript ecmascript-6

Answer 1

Answer №1

If the initial arg is considered an array

The concept can be best understood through a practical example

const x = [1,2,3,4];
const y = [...x];
x == y; // results in false
x === y; // results in false
x[0] == y[0]; // results in true
x[0] === y[0]; // results in true

Even though the array's content remains the same, it generates a new reference for the array itself. Therefore, it creates a duplicate of the original array without modifying it.

This scenario can be illustrated within a function as well

function example1(x) {
  x = [...x];
  x[0] = 0;
  return x;
}
function example2(x) {
  x[0] = 0;
  return x;
}

const a = [1,2,3];
console.log(a);
const b = example1(a);
// The original variable remains unchanged
console.log(a); // [1,2,3]
console.log(b); // [0,2,3]
const c = example2(a);
// The original variable is altered
console.log(a); // [0,2,3]
console.log(c); // [0,2,3]

Answer 2

If the initial arg is considered an array

The concept can be best understood through a practical example

const x = [1,2,3,4];
const y = [...x];
x == y; // results in false
x === y; // results in false
x[0] == y[0]; // results in true
x[0] === y[0]; // results in true

Even though the array's content remains the same, it generates a new reference for the array itself. Therefore, it creates a duplicate of the original array without modifying it.

This scenario can be illustrated within a function as well

function example1(x) {
  x = [...x];
  x[0] = 0;
  return x;
}
function example2(x) {
  x[0] = 0;
  return x;
}

const a = [1,2,3];
console.log(a);
const b = example1(a);
// The original variable remains unchanged
console.log(a); // [1,2,3]
console.log(b); // [0,2,3]
const c = example2(a);
// The original variable is altered
console.log(a); // [0,2,3]
console.log(c); // [0,2,3]

Why is it important to understand the meaning of variable = [...variable] in Javascript ES6?

Answer №1

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