JavaScript Tutorial/Operators/typeof — различия между версиями
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Текущая версия на 08:24, 26 мая 2010
Содержание
Get variable type
<html>
<head>
<title>A Simple Page</title>
<script language="JavaScript">
<!--
var x = "Hello", y;
alert("Variable x value is " + typeof(x));
alert("Variable y value is " + typeof(y));
alert("Variable z value is " + typeof(z));
// -->
</script>
</head>
<body>
</body>
</html>
The Typeof Operator
The typeof operator takes one parameter: the variable or value to check.
var sTemp = "test string";
alert(typeof sTemp);
alert(typeof 95);
Calling typeof on a variable or value returns one of the following values:
- "undefined" if the variable is of the Undefined type.
- "boolean" if the variable is of the Boolean type.
- "number" if the variable is of the Number type.
- "string" if the variable is of the String type.
- "object" if the variable is of a reference type or of the Null type.
typeof
Syntax
typeof(variable)
typeof a variable: number
<html>
<head>
<title>Debug Example</title>
<script type="text/javascript">
function aFunction(iNum1) {
if (typeof iNum1 == "number" ){
alert("number");
}
if ( typeof iNum1 == "string") {
alert("string");
}
}
aFunction("a");
aFunction(1);
</script>
</head>
<body>
</body>
</html>
typeof a variable: string
<html>
<head>
<title>Debug Example</title>
<script type="text/javascript">
function aFunction(iNum1) {
if (typeof iNum1 == "number" ){
alert("number");
}
if ( typeof iNum1 == "string") {
alert("string");
}
}
aFunction("a");
aFunction(1);
</script>
</head>
<body>
</body>
</html>