__spread Performance Issues

__spread

var tslib = require("tslib");
const { concat } = require('lodash')

var testPushES6 = function(abc) {
    var arr1 = [1,2,3,-1]
    var arr2 = [4,5,6,7,8,9,10,12,13,14,15,16,17,18,29,30,31,32,33,34,35,36,37,38,39,40]
    const arr = arr1.push(...arr2)
}

var testPush = function(abc) {
    var arr1 = [1,2,3,-1]
    var arr2 = [4,5,6,7,8,9,10,12,13,14,15,16,17,18,29,30,31,32,33,34,35,36,37,38,39,40]
    Array.prototype.push.apply(arr1, arr2)
}

var testPush2 = function(flag) {
    var arr1 = [1,2,3,-1]
    var arr2 = [4,5,6,7,8,9,10,12,13,14,15,16,17,18,29,30,31,32,33,34,35,36,37,38,39,40]
    arr1.push.apply(arr1, tslib.__spread(arr2));
}

var testConcat = function(abc) {
    var arr1 = [1,2,3,-1]
    var arr2 = [4,5,6,7,8,9,10,12,13,14,15,16,17,18,29,30,31,32,33,34,35,36,37,38,39,40]
    var arr  = arr1.concat(arr2)
  }

var testConcat = function(abc) {
    var arr1 = [1,2,3,-1]
    var arr2 = [4,5,6,7,8,9,10,12,13,14,15,16,17,18,29,30,31,32,33,34,35,36,37,38,39,40]
    var arr  = concat(arr1, arr2)
  }

var count = 1000000

var date = Date.now()
for (var i = 0; i < count; i++) {
  testPushES6()
}
// 136
console.log(Date.now() - date)

var date = Date.now()
for (var i = 0; i < count; i++) {
  testPush()
}
// 139
console.log(Date.now() - date)

var date = Date.now()
for (var i = 0; i < count; i++) {
  testPush2()
}
// 1005
console.log(Date.now() - date)

var date = Date.now()
for (var i = 0; i < count; i++) {
  testConcat()
}
// 310
console.log(Date.now() - date)

var date = Date.now()
for (var i = 0; i < count; i++) {
  testConcat2()
}
// 810
console.log(Date.now() - date)

Start by reproducing the benchmark in the issue and inspect the tslib.__spread helper it exercises. Compare its results and timing with the native spread, Array.prototype.push.apply, and concat cases shown; done would require an agreed performance improvement without changing behavior.