Extract variable

To extract a variable, you need to select the full expression that you would like to extract, and then invoke the refactor or extract context menu.

Extracting targets of method calls can change the 'this' reference

Consider the following example:

const anObject = {
    doSomething() {
        console.log({
            isObject: this === anObject,
            isGlobal: this === globalThis
        })
    }
}

anObject.doSomething(); // prints { isObject: true, isGlobal: false }

Extracting anObject.doSomething into a new variable extracted changes the this reference of the method call and its behavior:

const extracted = anObject.doSomething;
extracted();            // prints { isObject: false, isGlobal: true }

Assignment targets are not extracted

The left side of assignment expressions is not extracted, because it would change the program behavior.

Consider following example:

anObject.aProperty = 123; // assignment to anObject.aProperty

Extracting anObject.aProperty into a variable would mean that the assignment would change the variable, but not the object property:

const aVariable = anObject.aProperty;
aVariable = 123; // does not change anObject.aProperty

P42 does not extract such assignment targets.