ReferenceError: "x" is not defined
訊息
ReferenceError: "x" is not defined
錯誤類型
哪裡錯了?
有個地方參照到不存在的變數了。這個變數需要宣告、或確定在目前腳本、或在 scope (en-US) 裡可用。
備註: 如果要使用函式庫(例如 jQuery)的話,請確定在你使用諸如 $ 這樣的函式庫變數前,就已載入完畢。把載入函式庫的 <script>
標籤,放在你使用的程式碼之前。
實例
變數未宣告
foo.substring(1); // ReferenceError: foo is not defined
"foo" 變數在任何地方都沒被定義到。它需要字串使 String.prototype.substring()
(en-US) 得以運作。
var foo = "bar";
foo.substring(1); // "ar"
作用域錯誤
A variable need to be available in the current context of execution. Variables defined inside a function (en-US) cannot be accessed from anywhere outside the function, because the variable is defined only in the scope of the function
function numbers() {
var num1 = 2,
num2 = 3;
return num1 + num2;
}
console.log(num1); // ReferenceError num1 is not defined.
However, a function can access all variables and functions defined inside the scope in which it is defined. In other words, a function defined in the global scope can access all variables defined in the global scope.
var num1 = 2,
num2 = 3;
function numbers() {
return num1 + num2;
}
console.log(num1); // 2