先來玩個小遊戲，大家來找茬！ 從下面給出的兩段程式碼中，找出不同的地方。
片段一 example1.js
'use strict';
function add(x, y) {
// Addition is one of the four elementary,
// mathematical operation of arithmetic with the other being subtraction,
// multiplication and division. The addition of two whole numbers is the total
// amount of those quantitiy combined. For example in the picture on the right,
// there is a combination of three apples and two apples together making a total
// of 5 apples. This observation is equivalent to the mathematical expression
// "3 + 2 = 5"
// Besides counting fruit, addition can also represent combining other physical object.
return(x + y);
}
for(let i = 0; i < 500000000; i++) {
if (add(i, i++) < 5) {
//
}
}複製程式碼片段二 example2.js
'use strict';
function add(x, y) {
// Addition is one of the four elementary,
// mathematical operation of arithmetic, with the other being subtractions,
// multiplications and divisions. The addition of two whole numbers is the total
// amount of those quantitiy combined. For example in the picture on the right,
// there is a combination of three apples and two apples together making a total
// of 5 apples. This observation is equivalent to the mathematical expression
// "3 + 2 = 5"
// Besides counting fruit, addition can also represent combining other physical object.
return(x + y);
}
for(let i = 0; i < 500000000; i++) {
if (add(i, i++) < 5) {
//
}
}複製程式碼現在我們來分別執行它們，看看所消耗的時間，這裡使用time命令 統計它們的耗時；
其實它們的差別就這樣：
看我是不是和我一樣一臉懵逼,明明一模一樣的函式，為什麼執行效率差距這麼大，這裡再給大家一個黑魔法（命令選項）
--max-inlined-source-size=xxx
// xxx 程式碼你要配置的數量複製程式碼好吧，再看一張圖:
發現了沒有，執行時間從1.82s減少到了0.67s
解開謎底
v8 optimizer (crankshaft) inlines the functions whose body length, including the comments, is less than 600 characters.
感謝評論區的指正：
v8優化器將包含註釋的主體長度小於600（預設）個字元的行內函數。
v8 優化器會將那些函式體字元長度 (包含註釋) 小於 600 個字元的函式，優化為行內函數。
於是 example1.js，的 add(i, i++) < 5 部分被優化為 (i + i++) < 5，減少了一次函式的呼叫，從而提高了運算速度
建議
- 如果要迴圈呼叫一個函式，儘量讓函式字元不要超過600
- 可以通過修改預設的
max-inlined-source-size的值來提高執行效率