Function.apply()_javascript のパラメータ配列を使用して JavaScript プログラムのパフォーマンスを向上させるヒント

alert(Math.max(5,8))  //8 
alert(Math.max(5,7,9,3,1,6))  //9 

var arr=[5,7,9,1] 
alert(Math.max(arr))  //  这样却是不行的。一定要这样写 
function getMax(arr){ 
  var arrLen=arr.length; 
  for(var i=0,ret=arr[0];i<arrLen;i++){ 
    ret=Math.max(ret,arr[i]);     
  } 
  return ret; 
}  

function getMax2(arr){ 
  return Math.max.apply(null,arr) 
} 

var myArr=new Array() 
function fillRnd(arrLen){ //填入 arrLen个1-10的随机数字到数组 
  for(var i=0,arr=[];i<arrLen;i++){ 
    arr[i]=Math.ceil(Math.random()*10) 
  } 
  return arr 
} 
function getMax(arr){ 
  var arrLen=arr.length; 
  for(var i=0,ret=arr[0];i<arrLen;i++){ 
    ret=Math.max(ret,arr[i]);     
  } 
  return ret; 
} 
function getMax2(arr){ 
  return Math.max.apply(null,arr) 
} 
myArr=fillRnd(20*10000) //生成20万个随机数填到数组 
var t1=new Date() 
var max1=getMax(myArr) 
var t2=new Date() 
var max2=getMax2(myArr) 
var t3=new Date() 
if (max1!==max2) alert("error") 
alert([t3-t2,t2-t1])  //在我机器上 96,464 .不同的机器,结果可能有差异 

var arr1=[1,3,4]; 
var arr2=[3,4,5];

var arrLen=arr2.length 
for(var i=0;i<arrLen;i++){ 
  arr1.push(arr2[i]) 
}

Array.prototype.push.apply(arr1,arr2) 

var buf = new Array();for(var i = 0; i < 100; i++){ buf.push(i.toString());}var all = buf.join("");类型转换

var print; 
if(typeof document != "undefined" ){ 
  print = function(){ 
document.write(arguments[0]); 
} 
}else if(typeof WScript != "undefined" ){ 
  print = function(){ 
    WScript.Echo(arguments[0],arguments[1],arguments[2]); 
  } 
} 
function empty(){ 
} 
function benchmark(f){ 
  var i = 0; 
  var start = (new Date()).getTime(); 
  while(i < pressure){ 
    f(i++); 
  } 
  var end = (new Date()).getTime(); 
  WScript.Echo(end-start); 
} 
/* 
i=0 
start = (new Date()).getTime(); 
while(i < 60000){ 
  c = [i,i,i,i,i,i,i,i,i,i]; 
  i++; 
} 
end = (new Date()).getTime(); 
WScript.Echo(end-start); 
i=0 
start = (new Date()).getTime(); 
while(i < 60000){ 
  c = new Array(i,i,i,i,i,i,i,i,i,i); 
  i++; 
} 
var end = (new Date()).getTime(); 
WScript.Echo(end-start); 
*/ 
function internCast(i){ 
  return "" + i; 
} 
function StringCast(i){ 
  return String(i) 
} 
function newStringCast(i){ 
  return new String(i) 
} 
function toStringCast(i){ 
  return i.toString(); 
} 
function ParseInt(){ 
  return parseInt(j); 
} 
function MathFloor(){ 
  return Math.floor(j); 
} 
function Floor(){ 
  return floor(j); 
} 
var pressure = 50000; 
var a = ""; 
var floor = Math.floor; 
j = 123.123; 
print("-------------\nString Conversion Test"); 
print("The empty:", benchmark(empty)); 
print("intern:", benchmark(internCast)); 
print("String:"); 
benchmark(StringCast); 
print("new String:"); 
benchmark(newStringCast); 
print("toString:"); 
benchmark(toStringCast); 
print("-------------\nFloat to Int Conversion Test"); 
print("parseInt"); 
benchmark(ParseInt); 
print("Math.floor"); 
benchmark(MathFloor); 
print("floor") 
benchmark(Floor); 
function newObject(){ 
  return new Object(); 
} 
function internObject(){ 
  return {}; 
} 
print("------------\nliteral Test"); 
print("runtime new object", benchmark(newObject)); 
print("literal object", benchmark(internObject));  

for(var i=0;i<100;i++){ 
    arr[i]=0; 
  }

 var i = 0; 
  while(i < 100){ 
    arr[i++]=0; 
  } 

 var i = 0; 
  while(i < 100){ 
    arr[i]=0; 
    i++; 
  }

var i = 0; 
  var a; 
  while(i < 100){ 
    a = 0; 
    i++; 
  } 

 var a; 
  for(var i=0;i<100;i++){ 
    a = 0; 
  } 

  var a; 
  var i=0; 
  while(i<100){ 
    a=i; 
    i++; 
  } 

 var a; 
  var i=0; 
  while(i<100){ 
    a=i++; 
  } 

 var a; 
  for(var i=0;i<100;i++){ 
    a = i; 
  } 

 var a; 
  for(var i=0;i<100;){ 
    a = i++; 
  } 

for(var i=0;i<100;i++){  } 

  var i; 
  while(i<100){    i++;  }