Javascript 如何检查数组是否存在并以其他方式创建它？
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How to check if an array exists and create it otherwise?
提问by ajsie
How do I check if a specific array exists, and if not it will be created?
如何检查特定数组是否存在，如果不存在，将创建它？
回答by Rich
If you want to check whether an array x exists and create it if it doesn't, you can do
如果你想检查一个数组 x 是否存在，如果不存在就创建它，你可以这样做
x = ( typeof x != 'undefined' && x instanceof Array ) ? x : []
回答by Brian Campbell
var arr = arr || [];
回答by mynameistechno
const list = Array.isArray(x) ? x : [x];
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray
Or if xcouldbe an array and you want to make sure it is one:
或者如果x可以是一个数组并且您想确保它是一个：
const list = [].concat(x);
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/concat
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/concat
回答by Gumbo
You can use the typeofoperatorto test for undefinedand the instanceofoperatorto test if it's an instance of Array:
您可以使用typeof运算符来测试undefined并使用instanceof运算符来测试它是否是Array的实例：
if (typeof arr == "undefined" || !(arr instanceof Array)) {
var arr = [];
}
回答by CMS
If you want to check if the object is already an Array, to avoid the well known issuesof the instanceofoperator when working in multi-framed DOM environments, you could use the Object.prototype.toStringmethod:
如果要检查的对象已经是一个数组，避免了众所周知的问题的的instanceof多框DOM环境中工作时操作，您可以使用Object.prototype.toString方法：
arr = Object.prototype.toString.call(arr) == "[object Array]" ? arr : [];
回答by M RAHMAN
<script type="text/javascript">
array1 = new Array('apple','mango','banana');
var storearray1 =array1;
if (window[storearray1] && window[storearray1] instanceof Array) {
alert("exist!");
} else {
alert('not find: storearray1 = ' + typeof storearray1)
}
</script>
回答by slebetman
If you are talking about a browser environment then all global variables are members of the window object. So to check:
如果您在谈论浏览器环境，那么所有全局变量都是 window 对象的成员。所以要检查：
if (window.somearray !== undefined) {
somearray = [];
}
