The examples in this article share JavaScript programming learning skills for your reference. The specific content is as follows
1. Variable conversion
varmyVar="3.14159", str=""+myVar,//tostring int=~~myVar,//tointeger float=1*myVar,//tofloat bool=!!myVar,/*toboolean-anystringwithlength andanynumberexcept0aretrue*/ array=[myVar];//toarray
However, you must use the constructor to convert dates (new Date(myVar)) and regular expressions (new RegExp(myVar)). When creating regular expressions, use simplified forms such as /pattern/flags.
2. Round and convert to numerical value at the same time
//字符型变量参与运算时，JS会自动将其转换为数值型（如果无法转化，变为NaN） '10.567890'|0 //结果:10 //JS里面的所有数值型都是双精度浮点数,因此，JS在进行位运算时，会首先将这些数字运算数转换为整数，然后再执行运算 //|是二进制或，x|0永远等于x；^为异或，同0异1，所以x^0还是永远等于x；至于~是按位取反，搞了两次以后值当然是一样的 '10.567890'^0 //结果:10 -2.23456789|0 //结果:-2
3. Convert date to value
//JS本身时间的内部表示形式就是Unix时间戳，以毫秒为单位记录着当前距离1970年1月1日0点的时间单位 vard=+newDate();//1295698416792
4. Convert array-like object to array
vararr=[].slice.call(arguments)
下面的实例用的更绝
functiontest(){
varres=['item1','item2']
res=res.concat(Array.prototype.slice.call(arguments))//方法1
Array.prototype.push.apply(res,arguments)//方法2
}
5. Conversion between bases
(int).toString(16);//convertsinttohex,eg12=>"C" (int).toString(8);//convertsinttooctal,eg.12=>"14" parseInt(string,16)//convertshextoint,eg."FF"=>255 parseInt(string,8)//convertsoctaltoint,eg."20"=>16 将一个数组插入另一个数组指定的位置 vara=[1,2,3,7,8,9]; varb=[4,5,6]; varinsertIndex=3; a.splice.apply(a,Array.prototype.concat(insertIndex,0,b));
6. Delete array elements
vara=[1,2,3,4,5]; a.splice(3,1);//a=[1,2,3,5]
You may wonder why you should use splice instead of delete, because using delete will leave a hole in the array, and the subsequent subscripts will not be decremented.
7. Determine whether it is IE
varie=/*@cc_on!@*/false;
Such a simple sentence can determine whether it is ie, too. . .
In fact, there are more wonderful ways, please see below
//edithttp://www.lai18.com //貌似是最短的，利用IE不支持标准的ECMAscript中数组末逗号忽略的机制 varie=!-[1,]; //利用了IE的条件注释 varie=/*@cc_on!@*/false; //还是条件注释 varie//@cc_on=1; //IE不支持垂直制表符 varie='v'=='v'; //原理同上 varie=!+"v1";
The moment I learned this, I felt weak.
Use native methods as much as possible
To find the maximum number in a set of numbers, we might write a loop, for example:
varnumbers=[3,342,23,22,124];
varmax=0;
for(vari=0;i
if(numbers[i]>max){
max=numbers[i];
}
}
alert(max);
In fact, it can be implemented more easily using native methods
varnumbers=[3,342,23,22,124];
numbers.sort(function(a,b){returnb-a});
alert(numbers[0]);
Of course the simplest method is:
Math.max(12,123,3,2,433,4);//returns433
This is also possible now
[xhtml]view plaincopy Math.max.apply(Math,[12,123,3,2,433,4])//取最大值 Math.min.apply(Math,[12,123,3,2,433,4])//取最小值
8. Generate random numbers
Math.random().toString(16).substring(2);//toString()函数的参数为基底，范围为2~36。 Math.random().toString(36).substring(2);
Exchange the values of two variables without using third-party variables
a=[b,b=a][0];
9. Event delegation
js code is as follows:
//Classiceventhandlingexample
(function(){
varresources=document.getElementById('resources');
varlinks=resources.getElementsByTagName('a');
varall=links.length;
for(vari=0;i
//Attachalistenertoeachlink
links[i].addEventListener('click',handler,false);
};
functionhandler(e){
varx=e.target;//Getthelinkthatwasclicked
alert(x);
e.preventDefault();
};
})();
Use event delegation to write more elegantly:
(function(){
varresources=document.getElementById('resources');
resources.addEventListener('click',handler,false);
functionhandler(e){
varx=e.target;//getthelinktha
if(x.nodeName.toLowerCase()==='a'){
alert('Eventdelegation:'+x);
e.preventDefault();
}
};
})();
10. Check ie version
var_IE=(function(){
varv=3,div=document.createElement('div'),all=div.getElementsByTagName('i');
while(
div.innerHTML='',
all[0]
);
returnv>4?v:false;
}());
javaScript version detection
Do you know which version of Javascript your browser supports?
varJS_ver=[];
(Number.prototype.toFixed)?JS_ver.push("1.5"):false;
([].indexOf&&[].forEach)?JS_ver.push("1.6"):false;
((function(){try{[a,b]=[0,1];returntrue;}catch(ex){returnfalse;}})())?JS_ver.push("1.7"):false;
([].reduce&&[].reduceRight&&JSON)?JS_ver.push("1.8"):false;
("".trimLeft)?JS_ver.push("1.8.1"):false;
JS_ver.supports=function()
{
if(arguments[0])
return(!!~this.join().indexOf(arguments[0]+",")+",");
else
return(this[this.length-1]);
}
alert("LatestJavascriptversionsupported:"+JS_ver.supports());
alert("Supportforversion1.7:"+JS_ver.supports("1.7"));
11. Determine whether the attribute exists
//BAD:Thiswillcauseanerrorincodewhenfooisundefined
if(foo){
doSomething();
}
//GOOD:Thisdoesn'tcauseanyerrors.However,evenwhen
//fooissettoNULLorfalse,theconditionvalidatesastrue
if(typeoffoo!="undefined"){
doSomething();
}
//BETTER:Thisdoesn'tcauseanyerrorsandinaddition
//valuesNULLorfalsewon'tvalidateastrue
if(window.foo){
doSomething();
}
Sometimes we have deeper structures and need more appropriate inspections
//UGLY:wehavetoproofexistenceofevery
//objectbeforewecanbesurepropertyactuallyexists
if(window.oFoo&&oFoo.oBar&&oFoo.oBar.baz){
doSomething();
}
In fact, the best way to detect whether an attribute exists is:
if("opera"inwindow){
console.log("OPERA");
}else{
console.log("NOTOPERA");
}
12. Check whether the object is an array
varobj=[]; Object.prototype.toString.call(obj)=="[objectArray]";
The above is the entire content of this article. I hope it will be helpful to everyone in learning javascript programming.
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