The document analyzes the performance of different methods for merging arrays in JavaScript. It shows examples of using the concat() method, spread operator, and push.apply() method to merge the contents of two arrays. The push.apply() method had the best performance at 0.004ms, followed by the spread operator at 0.021ms, with concat() being the slowest at 0.080ms.

1. PERFORMANCE
ANALYSIS
IN MERGING
ARRAYS

2. let result = array1.concat(array2);
console.log(result); // [1 , 2 , 3 , 4, "a" , "b" , "c"]
let result = [...array1, ...array2]
console.log(result); // [1 , 2 , 3 , 4, "a" , "b" , "c"]
METHOD 1 - Using Concat() - 0.080ms
METHOD 2 - Using Spread Operator ... - 0.021ms
METHOD 3 - Using prototype.push() - 0.004ms
Array.prototype.push.apply(array1, array2);
console.log(array1); // [1 , 2 , 3 , 4, "a" , "b" , "c"]
// NOTE: the result is stored in 1st argument “array1”
let array1 = [1 , 2 , 3 , 4];
let array2 = ["a" , "b" , "c"];