Identifier resolution

As explained in Secrets of the JavaScript Ninja, Second Edition

The process of determining which binding a given identifier refers to in a particular program context.

When JavaScript encounters an identifier, it must determine which variable binding that name refers to. The running execution context performs this lookup through its lexical environment. section 5.3

Lookup follows the nested structure of the code:

• Check the current lexical environment for the identifier. section 5.4.2
• If it is not there, check outer environments in turn until a binding is found. section 5.4.2

Following the lookup

In the nested report and skulk example, intro is found in report’s environment, action in the outer skulk environment, and ninja in the global environment. section 5.4.2

Figure 5.9. How JavaScript engines resolve the values of variables

Trace how variable lookup moves through lexical environments to find a matching binding. section 5.4.2

How Secrets of the JavaScript Ninja, Second Edition covers it

How deep it goes

Traces lookup from the current lexical environment through outer environments, then turns to variable declaration forms.

Examples

Uses nested report and skulk functions to trace intro, action, and ninja to local, outer, and global environments.

What it assumes

Assumes familiarity with JavaScript function calls and execution contexts while explaining lexical-environment lookup.

What you can do after

Understand how JavaScript finds the binding for an identifier across nested lexical environments.

How it connects

Connects identifier resolution to execution contexts, lexical environments, and global environments.

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Related concepts

• lexical environmentuses · A structure that associates identifiers with bindings and provides the context for resolving names at a point in program execution.

This explainer was generated by Manning's knowledge graph from the text of Secrets of the JavaScript Ninja, Second Edition. The section links point to the parts of the book it draws on.