TypeError: "x" is (not) "y"

الرسالة

TypeError: Unable to get property {x} of undefined or null reference (Edge)
TypeError: "x" is (not) "y" (Firefox)

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

نوع الخطأ Error type

TypeError.

 ماذا حصل؟

There was an unexpected type. This occurs oftentimes with undefined or null values.

Also, certain methods, such as Object.create() or Symbol.keyFor(), require a specific type, that must be provided.

أمثلة

حالات غير صحيحة

// 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

حل المشكلة

لإصلاح مؤشر null إلى قيم undefined أو null ، يمكنك استخدام عامل التشغيل typeof ، على سبيل المثال.

if (typeof foo !== 'undefined') {
  // Now we know that foo is defined, we are good to go.
}

شاهد أيضاً

• undefined
• null