map vs forEach

forEach

var a=[1,2,3]var b=a.forEach(function(value,index,array){array[index]=value*value})a // [1, 4, 9]

map 回调函数需要return

var a=[1,2,3]var b=a.map(function(value,index,array){return value*value})a // [1, 2, 3]map不改变原数组b //[1, 4, 9]

map的另一用法，获取数组对象的某属性的所有值

var a=[{"u":"uu","i":"ii"},{"u":"uuu","i":"iii"}]var b=a.map(function(value,index,array){return value.u})b.join(",")"uu,uuu"