在 TypeScript 中测试字符串类型的数组
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Test for array of string type in TypeScript
提问by Sean Kearon
How can I test if a variable is an array of string in TypeScript? Something like this:
如何测试变量是否是 TypeScript 中的字符串数组？像这样的东西：
function f(): string {
var a: string[] = ["A", "B", "C"];
if (typeof a === "string[]") {
return "Yes"
}
else {
// returns no as it's 'object'
return "No"
}
};
TypeScript.io here: http://typescript.io/k0ZiJzso0Qg/2
TypeScript.io 在这里：http: //typescript.io/k0ZiJzso0Qg/2
Edit: I've updated the text to ask for a test for string[]. This was only in the code example previously.
编辑：我已更新文本以要求对字符串 [] 进行测试。这仅在之前的代码示例中。
回答by basarat
You cannot test for string[]in the general case but you can test for Arrayquite easily the same as in JavaScript https://stackoverflow.com/a/767492/390330
您无法string[]在一般情况下进行测试，但您可以Array像在 JavaScript 中一样轻松地进行测试https://stackoverflow.com/a/767492/390330
If you specifically want for stringarray you can do something like:
如果您特别想要string数组，您可以执行以下操作：
if (value instanceof Array) {
var somethingIsNotString = false;
value.forEach(function(item){
if(typeof item !== 'string'){
somethingIsNotString = true;
}
})
if(!somethingIsNotString && value.length > 0){
console.log('string[]!');
}
}
回答by grigson
Another option is Array.isArray()
另一种选择是Array.isArray()
if(! Array.isArray(classNames) ){
classNames = [classNames]
}
回答by axmrnv
Here is the most concise solution so far:
这是迄今为止最简洁的解决方案：
function isArrayOfStrings(value: any): boolean {
return Array.isArray(value) && value.every(item => typeof item === "string");
}
Note that value.everywill return truefor an empty array. If you need to return falsefor an empty array, you should add value.lengthto the condition clause:
请注意，这value.every将返回true一个空数组。如果你需要返回false一个空数组，你应该添加value.length到条件子句中：
function isNonEmptyArrayOfStrings(value: any): boolean {
return Array.isArray(value) && value.length && value.every(item => typeof item === "string");
}
There is no any run-time type information in TypeScript (and there won't be, see TypeScript Design Goals > Non goals, 5), so there is no way to get the type of an empty array. For a non-empty array all you can do is to check the type of its items, one by one.
TypeScript 中没有任何运行时类型信息（并且不会有，请参阅TypeScript 设计目标 > 非目标，5），因此无法获取空数组的类型。对于非空数组，您所能做的就是一一检查其项目的类型。
回答by Nicholas Boll
I know this has been answered, but TypeScript introduced type guards: https://www.typescriptlang.org/docs/handbook/advanced-types.html#typeof-type-guards
我知道这已经得到回答，但 TypeScript 引入了类型保护：https: //www.typescriptlang.org/docs/handbook/advanced-types.html#typeof-type-guards
If you have a type like: Object[] | string[]and what to do something conditionally based on what type it is - you can use this type guarding:
如果你有这样的类型：Object[] | string[]以及根据它是什么类型有条件地做某事 - 你可以使用这种类型保护：
function isStringArray(value: any): value is string[] {
if (value instanceof Array) {
value.forEach(function(item) { // maybe only check first value?
if (typeof item !== 'string') {
return false
}
})
return true
}
return false
}
function join<T>(value: string[] | T[]) {
if (isStringArray(value)) {
return value.join(',') // value is string[] here
} else {
return value.map((x) => x.toString()).join(',') // value is T[] here
}
}
There is an issue with an empty array being typed as string[], but that might be okay
将空数组输入为 存在问题string[]，但这可能没问题
回答by Sudarshana Dayananda
You can have do it easily using Array.prototype.some()as below.
您可以使用Array.prototype.some()以下方法轻松完成。
const isStringArray = (test: any[]): boolean => {
return Array.isArray(test) && !test.some((value) => typeof value !== 'string')
}
const myArray = ["A", "B", "C"]
console.log(isStringArray(myArray)) // will be log true if string array
I believe this approach is better that others. That is why I am posting this answer.
我相信这种方法比其他方法更好。这就是我发布这个答案的原因。
回答by Tcanarchy
Try this:
尝试这个：
if (value instanceof Array) {
alert('value is Array!');
} else {
alert('Not an array');
}
回答by hans
there is a little problem here because the
这里有一个小问题，因为
if (typeof item !== 'string') {
return false
}
will not stop the foreach. So the function will return true even if the array does contain none string values.
不会停止 foreach。因此，即使数组不包含任何字符串值，该函数也将返回 true。
This seems to wok for me:
这似乎对我有用：
function isStringArray(value: any): value is number[] {
if (Object.prototype.toString.call(value) === '[object Array]') {
if (value.length < 1) {
return false;
} else {
return value.every((d: any) => typeof d === 'string');
}
}
return false;
}
Greetings, Hans
问候，汉斯
