js 数组合并

1、循环插入

　　for (var i=0; i < b.length; i++) {
　　　　a.push( b[i] );
　　}

2、 a.push.apply(a,b); 　

　　b.unshift.apply( b, a );

　　例如：　a.push.apply(a,[4,5,6]); 等同于 a.push(4,5,6);

3、 let c = a.concat( b );

4、ES5// `b` o

　a; // [1,2,3,4,5,6,7,8,9,"foo","bar","baz","bam","bun","fun"]

　// or `a` into `b`:
　b = a.reduceRight( function(coll,item){
　coll.unshift( item );
　return coll;
　}, b );

　b; // [1,2,3,4,5,6,7,8,9,"foo","bar","baz","bam","bun","fun"]

5、避免数组最大长度限制

　　function combineInto(a,b) {
    　　for (let i=0; i < a.length; i=i+5000) {
        　　b.unshift.apply( b, a.slice( i, i+5000 ) );
   　　 }
　　}