JavaScript中几种清空变量的方式性能对比

JavaScript中有几种常用的清空变量的方式：delete、设为null、设为undefined。
它们的性能差异如何呢？

结论

赋值为undefined或null，比delete快近70倍！！
并且也没有看出明显的内存差异。

delete

正向delete

(()=>{
  let totalTime = 0, N=10;
  for(let n=0; n<N; ++n){
    let a = {};
    for(let i=0; i<1000000; ++i){
     a[i] = i;
    }
    let startTime = Date.now();
    for(let i=0; i<1000000; ++i){
     delete a[i];
    }
    totalTime += Date.now() - startTime;
    a;
  }
  console.log(`avg ${totalTime/N}ms in ${N} times`);
})()

结果

avg 67.5ms in 10 times

反向delete

(()=>{
  let totalTime = 0, N=10;
  for(let n=0; n<N; ++n){
    let a = {};
    for(let i=0; i<1000000; ++i){
     a[i] = i;
    }
    let startTime = Date.now();
    for(let i=1000000-1; i>-1; --i){
     delete a[i];
    }
    totalTime += Date.now() - startTime;
    a;
  }
  console.log(`avg ${totalTime/N}ms in ${N} times`);
})()

结果

avg 64.4ms in 10 times

结论

delete 反向好像比正向快那么一丁点

set to undefined

正向

(()=>{
  let totalTime = 0, N=10;
  for(let n=0; n<N; ++n){
    let a = {};
    for(let i=0; i<1000000; ++i){
     a[i] = i;
    }
    let startTime = Date.now();
    for(let i=0; i<1000000; ++i){
     a[i] = undefined;
    }
    totalTime += Date.now() - startTime;
    a;
  }
  console.log(`avg ${totalTime/N}ms in ${N} times`);
})()

结果!!!!!

avg 0.8ms in 10 times

（正文完）