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JavaScript 提供了一种方法来测试变量的类型。然而,其结果可能会让人迷惑 - 例如,一个数组的类型是 `object`。 当试图检测一个特定值的类型时,常见的做法是使用 `typeof` 运算符。 ~~~ // Testing the type of various variables. var myFunction = function() { console.log( "hello" ); }; var myObject = { foo: "bar" }; var myArray = [ "a", "b", "c" ]; var myString = "hello"; var myNumber = 3; var myRegExp = /(\w+)\s(\w+)/; typeof myFunction; // "function" typeof myObject; // "object" typeof myArray; // "object" -- Careful! typeof myString; // "string" typeof myNumber; // "number" typeof null; // "object" -- Careful! typeof undefined; // "undefined" typeof meh; // "undefined" -- undefined variable. typeof myRegExp; // "function" or "object" depending on environment. if ( myArray.push && myArray.slice && myArray.join ) { // probably an array (this is called "duck typing") } if ( Object.prototype.toString.call( myArray ) === "[object Array]" ) { // Definitely an array! // This is widely considered as the most robust way // to determine if a specific value is an Array. } ~~~