解构变量性能

时间:2017-11-03 15:39:34

标签: javascript reactjs ecmascript-6 destructuring

写作之间是否有性能差异

const color = props.color;

VS

const { color } = props;

另外,如果我们在参数签名中进行结构化,我们是否会获得或失去任何表现?见例3

我认为在这种情况下,example3是编写函数的最佳方法吗?

功能性反应组分示例:

const example1 = (props) => {
  const color = props.color;
  // I know I could also just write style={{ color: props.color }}
  // but for arguments sake lets say I want to write it like this.
  return <h1 style={{ color }}>Hello</h1>;
};

const example2 = (props) => {
  const { color } = props;
  return <h1 style={{ color }}>Hello</h1>;
};

const example3 = ({ color }) => {
  return <h1 style={{ color }}>Hello</h1>;
};

2 个答案:

答案 0 :(得分:9)

编译器/编译器不一定会删除解构赋值,因为所有常绿浏览器自2020年起都支持本机解构。根据,有证据表明,至少到2018年,V8中由解构赋值生成的字节码。比传统的函数参数更冗长:

功能参数:

function add(number1, number2){
  return number1 + number2;
}
const result = add(1,5);

输出字节码:

[generating bytecode for function: add]
Parameter count 3
Frame size 0
   74 E> 0x2a2a0affd2a2 @    0 : 91                StackCheck 
   96 S> 0x2a2a0affd2a3 @    1 : 1d 02             Ldar a1
  111 E> 0x2a2a0affd2a5 @    3 : 2b 03 00          Add a0, [0]
  121 S> 0x2a2a0affd2a8 @    6 : 95                Return 
Constant pool (size = 0)
Handler Table (size = 16)

结构化分配:

function add({number1, number2}){
  return number1 + number2;
}
const result = add({number1: 1, number2: 5});

输出字节码:

[generating bytecode for function: add]
Parameter count 2
Frame size 40
   74 E> 0x2c1d63b7d312 @    0 : 91                StackCheck 
         0x2c1d63b7d313 @    1 : 1f 02 fb          Mov a0, r0
         0x2c1d63b7d316 @    4 : 1d fb             Ldar r0
         0x2c1d63b7d318 @    6 : 89 06             JumpIfUndefined [6] (0x2c1d63b7d31e @ 12)
         0x2c1d63b7d31a @    8 : 1d fb             Ldar r0
         0x2c1d63b7d31c @   10 : 88 10             JumpIfNotNull [16] (0x2c1d63b7d32c @ 26)
         0x2c1d63b7d31e @   12 : 03 3f             LdaSmi [63]
         0x2c1d63b7d320 @   14 : 1e f8             Star r3
         0x2c1d63b7d322 @   16 : 09 00             LdaConstant [0]
         0x2c1d63b7d324 @   18 : 1e f7             Star r4
         0x2c1d63b7d326 @   20 : 53 e8 00 f8 02    CallRuntime [NewTypeError], r3-r4
   76 E> 0x2c1d63b7d32b @   25 : 93                Throw 
   76 S> 0x2c1d63b7d32c @   26 : 20 fb 00 02       LdaNamedProperty r0, [0], [2]
         0x2c1d63b7d330 @   30 : 1e fa             Star r1
   85 S> 0x2c1d63b7d332 @   32 : 20 fb 01 04       LdaNamedProperty r0, [1], [4]
         0x2c1d63b7d336 @   36 : 1e f9             Star r2
   98 S> 0x2c1d63b7d338 @   38 : 1d f9             Ldar r2
  113 E> 0x2c1d63b7d33a @   40 : 2b fa 06          Add r1, [6]
  123 S> 0x2c1d63b7d33d @   43 : 95                Return 
Constant pool (size = 2)
Handler Table (size = 16)

字节代码行的数量从功能参数的4个显着增加到结构化分配的19个。综上所述,截至2018年,V8中的非结构化分配比传统函数参数的计算效率更低。就内存空间利用率而言,答案要复杂一些,可以参考here

这可能是过早的优化,但是在计算繁重的代码时,建议不要使用解构分配。

答案 1 :(得分:3)

由于您的代码将被编译/缩小等等,因此无法解决任何性能问题。

请注意,使用React,您的代码将被转换为与

相同的代码

const color = props.color

检查babel compiler online tester

上的结果