javascript - js对象 属性的访问和创建

问题描述

一个有意思的问题：

var a = new Object(); var b = new Object(); var c = new Object(); c[a] = a; c[b] = b; console.log(c[a] === a); //输出什么? ---> falseconsole.log(c[b] === b); //输出什么? ---> true

var a = new Object(); var b = new Object(); var c = new Object(); c.a=a; c.b=b; console.log(c.a === a); //输出什么? ---> trueconsole.log(c.b === b); //输出什么? ---> true

这里其实涉及到的就是[]运算符 和.运算符 相关知识。

附上相关规则和网址,你们自己研究吧：

MemberExpression : MemberExpression [ Expression ]

Let baseReference be the result of evaluating MemberExpression.

Let baseValue be GetValue(baseReference).

ReturnIfAbrupt(baseValue).

Let propertyNameReference be the result of evaluating Expression.

Let propertyNameValue be GetValue(propertyNameReference).

ReturnIfAbrupt(propertyNameValue).

Let bv be RequireObjectCoercible(baseValue).

ReturnIfAbrupt(bv).

Let propertyKey be ToPropertyKey(propertyNameValue).

ReturnIfAbrupt(propertyKey).

If the code matched by the syntactic production that is being evaluated is strict mode code, let strict be true, else let strict be false.

Return a value of type Reference whose base value is bv and whose referenced name is propertyKey, and whose strict reference flag is strict.

MemberExpression : MemberExpression . IdentifierName

Let baseReference be the result of evaluating MemberExpression.

Let baseValue be GetValue(baseReference).

ReturnIfAbrupt(baseValue).

Let bv be RequireObjectCoercible(baseValue).

ReturnIfAbrupt(bv).

Let propertyNameString be StringValue of IdentifierName

If the code matched by the syntactic production that is being evaluated is strict mode code, let strict be true, else let strict be false.

Return a value of type Reference whose base value is bv and whose referenced name is propertyNameString, and whose strict reference flag is strict.

CallExpression : CallExpression [ Expression ]

Is evaluated in exactly the same manner as MemberExpression : MemberExpression [ Expression ] except that the contained CallExpression is evaluated in step 1.

CallExpression : CallExpression . IdentifierName

Is evaluated in exactly the same manner as MemberExpression : MemberExpression . IdentifierName except that the contained CallExpression is evaluated in step 1.

ECMAScript 2015 #sec-property-accessors

问题解答

其实就是个 Object toString 的问题。