メッセージ
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) Examples: 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
エラータイプ
何がうまくいかなかったのか?
例
無効なケース
// 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
問題解決
undefined
か null
の null pointer アクセスを修正するには、たとえば typeof 演算子を使用できます。
if (typeof foo !== 'undefined') {
// Now we know that foo is defined, we are good to go.
}