検証コード
javascript
(function() {
console.time('push');
var array = [];
for (var i=0;i<100000000;i++) {
array.push(i);
}
console.timeEnd('push');
})();
(function() {
console.time('length');
var array = [];
for (var i=0;i<100000000;i++) {
array[array.length] = i;
}
console.timeEnd('length');
})();
結果
Chrome 51.0.2704.63 (64-bit)
push: 1577.093ms
length: 1537.691ms
Firefox 46.0.1
push: 1812.18ms
length: 1866.65ms