2.5 in 运算符 in运算符用于检查对象是否包含某个属性(注意,检查的是键名,不是键值),如果包含就返回true,否则返回false。 varobj = { p:1};'p'inobj// true in运算符的一个问题是,它不能识别哪些属性是对象自身的,哪些属性是继承的。 varobj = {};'toString'inobj// true 上面代码中,toString方法不是...
参见 Class declaration Class constructor 术语:constructorHelp improve MDN Was this page helpful to you? YesNoLearn how to contribute. This page was last modified on 2025年3月8日 by MDN contributors. View this page on GitHub • Report a problem with this content ...
it is important to understand that objects (including arrays and functions) assigned to a variable using const are still mutable. Using the const declaration only prevents reassignment of the variable identifier. 重要的是要理解,使用const分配给变量的对象(包括数组和函数)仍然是可变的。使用const声明只能...
所有函数声明(FunctionDeclaration, FD) —由名称和对应值(函数对象(function-object))组成一个变量对象的属性被创建;如果变量对象已经存在相同名称的属性,则完全替换这个属性。 所有变量声明(var, VariableDeclaration) — 由名称和对应值(undefined)组成一个变量对象的属性被创建;如果变量名称跟已经声明的形式参数或函数...
function declarations (FunctionDeclaration, in abbreviated form FD); and function formal parameters declared in the context. 举个例子,可以用ECMAScript的对象来表示变量对象: <pre>VO = {}; </pre> VO同时也是一个执行上下文的属性: <pre>activeExecutionContext = { ...
toString()Converts an object to a string and returns the result valueOf()Returns the primitive value of an object values()Returns an array of the property values of an object ❮ PreviousNext ❯ Track your progress - it's free! Log inSign Up...
Again, using Object.setPrototypeOf() may have adverse performance effects, so make sure it happens immediately after the constructor declaration and before any instances are created — to avoid objects being "tainted". Note: Manually updating or setting the constructor can lead to different and som...
ForIn FunctionConstructor FunctionDeclaration FunctionExpression FunctionObject FunctionObject Methods FunctionPrototype FunctionWrapper GlobalObject Globals GlobalScope Hide IActivationObject IAuthorServices IColorizeText IDebugConvert IDebugConvert2 IDebuggerObject ...
declareSets or retrieves whether an object is only a declaration (it isn't downloaded until it's needed). dirSets or retrieves the text direction as related to thelangproperty. disabledSets or retrieves the state of an object for user interaction. ...
declareNot supported in HTML5. formReturns a reference to the object's parent form heightSets or returns the height of the object hspaceNot supported in HTML5. Usestyle.margininstead. Sets or returns the horizontal margin of the object