Errors: Unexpected type
Errors: Unexpected type
信息
TypeError: "x" is (not) "y"
Examples:
TypeError: "x" is undefined
TypeError: "x" is null
TypeError: "undefined" is not an object
TypeError: "x" is not an object or null
TypeError: "x" is not a symbol
错误类型
TypeError.
哪里出错了?
有一个意想不到的类型。这会产生undefined或null值。
另外，必须提供某些方法，例如Object.create()或Symbol.keyFor()需要特定的类型。
示例
无效的情况
// undefined and null cases on which the substring method won't work
var foo = undefined;
foo.substring(1 // TypeError: foo is undefined
var foo = null;
foo.substring(1 // TypeError: foo is null
// Certain methods might require a specific type
var foo = {}
Symbol.keyFor(foo // TypeError: foo is not a symbol
var foo = 'bar'
Object.create(foo // TypeError: "foo" is not an object or null
解决这个问题
例如，要修复空值指针undefined或null值，可以使用typeof运算符。
if (typeof foo !== 'undefined') {
// Now we know that foo is defined, we are good to go.
}
