TypeError: join 不是 JavaScript 中的函数

TypeError: join 不是 JavaScript 中的函数

TypeError: join is not a function in JavaScript

“TypeError: join is not a function” 当我们join()
在一个不是数组的值上调用方法时发生。

要解决该错误，请确保仅join在有效数组上调用该方法。

下面是错误如何发生的示例。

const arr = {};

// ⛔️ Uncaught TypeError: join is not a function
const result = arr.join(',');

我们

在一个对象上调用了Array.join()方法并返回了错误。

Array.join()只在数组上调用方法

要解决该错误，console.log您调用该join方法的值并确保它是一个有效的数组。

const arr = ['bobby', 'hadz', 'com'];

const result = arr.join(',');

// 👇️ "bobby,hadz,com"
console.log(result);

在调用之前检查该值是否为数组join()

您可以使用Array.isArray
方法有条件地检查值是否为数组
。

const arr = null;

const result = Array.isArray(arr) ? arr.join(',') : "";

console.log(result); // 👉️ ""

if/else我们使用了三元运算符，它与语句非常相似。

如果值是一个数组，我们返回调用该join方法的结果。否则，我们返回一个空字符串。

这样，即使值不是数组，您也不会收到错误。

您还可以使用简单的if语句来检查值是否为数组。

const arr = null;

let result = '';

if (Array.isArray(arr)) {
  result = arr.join(',');
}

console.log(result); // 👉️ ""

如果arr变量存储一个数组，if块将在我们调用
join()方法的地方运行。

在调用之前将值转换为数组join()

If you have an array-like object, use the Array.from() method to convert it to
an array before calling join().

const set = new Set(['bobby', 'hadz', 'com']);

const result = Array.from(set).join(',');
console.log(result); // 👉️ "bobby,hadz,com"

We used the Array.from() method to convert a Set object to an array to be
able to use the Array.join() method.

You could achieve the same result by using the spread syntax (…).

const set = new Set(['one', 'two', 'three']);

const result = [...set].join(',');
console.log(result); // 👉️ "one,two,three"

If you have an object that has an array property, access the property before
calling the join() method.

const obj = {
  site: ['bobby', 'hadz', 'com'],
};

const result = obj.site.join(', ');
console.log(result); // 👉️ bobby, hadz, com

We accessed a property on the object that stores an array to be able to call the
join() method.

If the value is fetched from a remote server, make sure it is of the type you
expect it to be by logging it to the console.

Also, ensure you have parsed it to a native JavaScript array before calling the
join method on it.

The
Array.join()
method concatenates all of the elements in an array using a separator.

The only argument the Array.join() method takes is a separator – the string
used to separate the elements of the array.

If a value for the separator argument is omitted, the array elements are
joined with a comma ,.

If the separator argument is set to an empty string, the array elements are
joined without any characters in between them.

Conclusion #

The “TypeError: join is not a function” occurs when we call the join()
method on a value that is not an array. To solve the error, make sure to only
call the join method on valid arrays.