com.google.javascript.jscomp

Class CheckGlobalThis

java.lang.Object

com.google.javascript.jscomp.CheckGlobalThis

All Implemented Interfaces:

NodeTraversal.Callback

final class CheckGlobalThis
extends java.lang.Object
implements NodeTraversal.Callback

Checks for certain uses of the this keyword that are considered unsafe because they are likely to reference the global this object unintentionally.

A use of this is considered unsafe if it's on the left side of an assignment or a property access, and not inside one of the following:

1. a prototype method
2. a function annotated with @constructor
3. a function annotated with @this.
4. a function where there's no logical place to put a this annotation.

Note that this check does not track assignments of this to variables or objects. The code

 function evil() {
   var a = this;
   a.useful = undefined;
 }
 

will not get flagged, even though it is semantically equivalent to

 function evil() {
   this.useful = undefined;
 }
 

which would get flagged.

Field Summary

Fields

Modifier and Type	Field and Description
private Node	assignLhsChild If assignLhsChild != null, then the node being traversed is a descendant of the first child of an ASSIGN node.
private AbstractCompiler	compiler
(package private) static DiagnosticType	GLOBAL_THIS

Constructor Summary

Constructors

Constructor and Description
CheckGlobalThis(AbstractCompiler compiler)

Method Summary

Modifier and Type	Method and Description
private boolean	shouldReportThis(Node n)
boolean	shouldTraverse(NodeTraversal t, Node n, Node parent) Since this pass reports errors only when a global this keyword is encountered, there is no reason to traverse non global contexts.
void	visit(NodeTraversal t, Node n, Node parent) Visits a node in postorder (after its children have been visited).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

GLOBAL_THIS

static final DiagnosticType GLOBAL_THIS

compiler

private final AbstractCompiler compiler

assignLhsChild

private Node assignLhsChild

If assignLhsChild != null, then the node being traversed is a descendant of the first child of an ASSIGN node. assignLhsChild's parent is this ASSIGN node.

Constructor Detail

CheckGlobalThis

CheckGlobalThis(AbstractCompiler compiler)

Method Detail

shouldTraverse

public boolean shouldTraverse(NodeTraversal t,
                              Node n,
                              Node parent)

Since this pass reports errors only when a global this keyword is encountered, there is no reason to traverse non global contexts.

Specified by:

shouldTraverse in interface NodeTraversal.Callback

Returns:

whether the children of this node should be visited

visit

public void visit(NodeTraversal t,
                  Node n,
                  Node parent)

Description copied from interface: NodeTraversal.Callback

Visits a node in postorder (after its children have been visited). A node is visited only if all its parents should be traversed (NodeTraversal.Callback.shouldTraverse(NodeTraversal, Node, Node)).

Implementations can have side effects (e.g. modifying the parse tree).

Specified by:

visit in interface NodeTraversal.Callback

shouldReportThis

private boolean shouldReportThis(Node n)