TypeError: can't access property "x" of "y"
エラーメッセージ
js
TypeError: Unable to get property {x} of undefined or null reference (Edge)
TypeError: can't access property {x} of {y} (Firefox)
TypeError: {y} is undefined, can't access property {x} of it (Firefox)
TypeError: {y} is null, can't access property {x} of it (Firefox)
例:
TypeError: x is undefined, can't access property "prop" of it
TypeError: x is null, can't access property "prop" of it
TypeError: can't access property "prop" of undefined
TypeError: can't access property "prop" of null
エラーの種類
エラーの原因
例
無効な場合
js
// undefined and null cases on which the substring method won't work
var foo = undefined;
foo.substring(1); // TypeError: x is undefined, can't access property "substring" of it
var foo = null;
foo.substring(1); // TypeError: x is null, can't access property "substring" of it
問題の修正
undefined
か null
のヌルポインターアクセスを修正するには、たとえば typeof 演算子を使用することができます。
js
if (typeof foo !== 'undefined') {
// Now we know that foo is defined, we are good to go.
}