ECMAScript（ECMA-262 5.1）中`reference`的“基本值”是什么？

Question

I've been trying to understand how this value is set in javascript, and found ECMAScript Language Specification pretty much helpful. I was reading section 8.7 reference specification type and found that reference in ECMAScript is made of 3 component, base value , referenced name , strict reference flag to understand section 11.2.3 .

I can assume what are referenced name and strict reference flag from their name, but i don't understand what is the base value . The document says that base value is either undefined , String , Boolean , Number and Object , but it does not say how it is set and what it is. I am guessing it is something similar to context object. Could anyone explain?

Answer 1

Yes, the base value is the context in which the referenced name lives.

For an object property, this would be the object (see §8.12 Object internal methods for setter/getter operations). For a variable, this would be the variable environment ( §10.2.1 Environment records ). For an unresolvable reference (the things that throw reference errors except when supplied to typeof ), this would be undefined .

it does not say how it is set

Reference values are only constructed by very few operations:

• identifier reference expressions , that resolve the identifier in the current lexical environment (or one of its parents)
• property accessor expressions , ie the .… and […] operators
• function calls to host functions are permitted to return them, but such don't exist .