JavaScript内置对象

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向上取整：Math.ceil()
document.wrie(Math.ceil(-9.3)+”“);
document.wtite(Math.ceil(7.8));

运行结果：-9         8

向下取整：Math.floor()
document.write(Math.floor(-9.3)+”“);
document.write(Math.floor(7.8));

 运行结果：-10          7

四舍五入：Math.round()
document.write(Math.round(-9.3)+”“);
document.write(Math.round(-9.9)+”“);
document.write(Math.round(7.8));

  运行结果：-9          -10          8

数组连接：concat()
var mya1=new Array(“Hello!”);
var mya2=new Array(“I”,”love”);
var mya3=new Array(“JavaScript”,”!”);
var mya4=mya1.concat(mya2,mya3);
document.write(mya4);

   运行结果：Hello!,I,love,JavaScript,!    var myarr1=new Array("010");    var myarr2=new Array("-","43555");    document.write(myarr1.concat(myarr2));    运行结果：010，-，43555

指定空格符连接数组元素：join()
var myarr=new Array(3);
myarr[0]=”I”;
myarr[1]=”love”;
myarr[2]=”javascript”;
document.write(myarr.join());
document.write(myarr.join(“.”));

      运行结果：I,love,javascript               I.love.javascript      var num1=new Array("86","010");      var num2=new Array("84697581");      var num3=num1.concat(num2);      document.write(num3.join("-"));      运行结果：86-01-084697581

颠倒数组元素顺序：reverse()
var myarr1=[“I”,”love”,”you”];
document.write(myarr1.reverse());

       运行结果：you,love,I

选定元素：slice()
var myarr1=[“I”,”love”,”you”];
document.write(myarr1.slice(1,3));

        运行结果：love,you

数组排序：sort()
function sortNum(a,b){
return a-b; //升序降序为：b-a;
}
var myarr=new Array(“80”,”16”,”50”,”6”,”100”,”1”);
document.write(myarr.sort(sortNum));

         运行结果：1,6,16,50,80,100

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