ie8支持foreach

if ( !Array.prototype.forEach ) {    Array.prototype.forEach = function forEach( callback, thisArg ) {        var T, k;        if ( this == null ) {            throw new TypeError( "this is null or not defined" );        }        var O = Object(this);        var len = O.length >>> 0;        if ( typeof callback !== "function" ) {            throw new TypeError( callback + " is not a function" );        }        if ( arguments.length > 1 ) {            T = thisArg;        }        k = 0;        while( k < len ) {            var kValue;            if ( k in O ) {                kValue = O[ k ];                callback.call( T, kValue, k, O );            }            k++;        }    };}