forEach兼容ie8

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++;

        }

    };

}