4.1 Primary Expressions
Literals are constant values that are embedded directly in your program. They look like these:
1.23 // A number literal "hello" // A string literal /pattern/ // A regular expression literal
true // Evalutes to the boolean true value false // Evaluates to the boolean false value null // Evaluates to the null value this // Evaluates to the "current" object
We learned about true, false, and null in §3.3 and §3.4 . Unlike the other keywords, thisis not a constant—it evaluates to different values in different places in the program. The this keyword is used in object-oriented programming. Within the body of a method, this evaluates to the object on which the method was invoked. See §4.5 , Chap ter 8 (especially §8.2.2 ), and Chapter 9 for more on this.
Finally, the third type of primary expression is the bare variable reference:
// Evaluates to the value of the variable i. sum // Evaluates to the value of the variable sum. undefined // undefined is a global variable, not a keyword like null.