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Using the Spread Operator to Evaluate Arrays In-Place

rthefounding profile image Randy Rivera ・1 min read

ES6 introduces the spread operator, which allows us to expand arrays and other expressions in places where multiple parameters or elements are expected.

  • Math.max() expects comma-separated arguments, but not an array. The spread operator makes this syntax much better to read and maintain.
const arr = [50, 10, 23, 234, 54];
const maxNum = Math.max(...arr);

 console.log(maxNum); will display 234
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...arr returns an unpacked array. In other words, it spreads the array. However, the spread operator only works in-place, like in an argument to a function or in an array literal.

const arr1 = ['JAN', 'FEB', 'MAR', 'APR', 'MAY'];
let arr2;

arr2 = [...arr1];  
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[ 'JAN', 'FEB', 'MAR', 'APR', 'MAY' ]
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Here we copied all contents of arr1 into another array arr2 using the spread operator.

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