Learning Notes

# push() is faster than concat()

# conclusion

OK, briefly, I recommend you to use Array.prototype.push(arr1, arr2) instead of arr1.concat(arr2) when merge arrays. And you can take ES6 to simplify the push methods: arr1.push(...arr2).

# How is it happens

# concat() naive implementation

// create a new array
var arr3 = []

for(var i = 0;i < arr1.length; i++){
  arr3[i] = arr1[i]
}

for(var i = 0;i < arr2.length; i++){
  arr3[arr1.length + i] = arr2[i]
}
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# push() naive implementation

for (var i = 0; i<arr2.length; i++){
  arr1[arr1.length + i] = arr2[i]
}
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As we can see, push() just has less for implementation than concat() which makes it faster.

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