.push() 将多个对象放入 JavaScript 数组返回“未定义”
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.push() multiple objects into JavaScript array returns 'undefined'
提问by MFrazier
When I add items to the beats array and then console.log the User, I'm getting the correct number of items in the array. But when I check .length, I always get 1.
Trying to call the index will always give me 'undefined' like so:
Tom.beats[1]I think I'm missing something obvious, but this is beating me. I suspect that I'm misusing the .pushmethod but I'm unsure. Any help is greatly appreciated!
(using Chrome dev tools)
当我将项目添加到 beats 数组然后 console.log 用户时，我得到了数组中正确数量的项目。但是当我检查 .length 时，我总是得到 1。尝试调用索引总是会给我 'undefined' 像这样：Tom.beats[1]我想我遗漏了一些明显的东西，但这让
我很失望。我怀疑我滥用了该.push方法，但我不确定。任何帮助是极大的赞赏！（使用 Chrome 开发工具）
//The USER
function User(name, role){
this.beats = [ ];
this.name = name;
this.role = role;
// add beats to beats array
this.addBeats = function(beats){
return this.beats.push(beats);
};
}
// Three New Instances. Three New Users.
var Mal = new User("Mal", "Rapper");
Mal.addBeats(["love", "cash"]);
var Dan = new User("Dan", "Producer");
Dan.addBeats(["cake", "dirt", "sally-mae"]);
var Tom = new User("Tom", "Producer");
Tom.addBeats(["Fun", "Little", "Samsung", "Turtle", "PC"]);
// Check for position in beats array
console.log(Tom.beats);
console.log(Mal.beats);
console.log(Dan.beats);
console.log(Mal.beats[1]);
console.log(Dan.beats[1]);
console.log(Tom.beats[1]);
回答by kay - SE is evil
Array.push(...)takes multiple arguments to append to the list. If you put them in an array itself, this very array of "beats" will be appended.
Array.push(...)将多个参数附加到列表中。如果你把它们放在一个数组中，这个“节拍”数组将被附加。
Array.concat(...)is most likely not what you are looking for, because it generates a new array instead of appending to the existing one.
Array.concat(...)很可能不是您要查找的内容，因为它会生成一个新数组而不是附加到现有数组。
You can use [].push.apply(Array, arg_list)to append the items of the argument list:
您可以使用[].push.apply(Array, arg_list)附加参数列表的项目：
this.addBeats = function(beats) {
return [].push.apply(this.beats, beats);
};
回答by Ashley Coolman
Spread operator
展开运算符
In environments that support the spread operatoryou may now do the following:
在支持扩展运算符的环境中，您现在可以执行以下操作：
this.addBeats = function (beats) {
return this.beats.push(...beats);
};
Or if you need more control for overwriting etc
或者，如果您需要更多控制覆盖等
this.addBeats = function(beats) {
return this.beats.splice(this.beats.length, null, ...beats);
};
回答by jmulligan
addBeats() should concat this.beats with the beats parameter.
addBeats() 应该将 this.beats 与 beats 参数连接起来。
