Values and Variables In JavaScript, a piece of information is a value . There are different kinds of values; the kind you're most familiar with are numbers . A string value is a word or words enclosed in quotes. Other kinds of JavaScript values are listed in Table 1.2 . Table 1.2. Value Types Type | Description | Example | Number | Any numeric value | 3.141592654 | String | Characters inside quote marks | "Hello, world!" | Boolean | True or False | true | Null | Empty and meaningless | | Object | Any value associated with the object | | Function | Value returned by a function | | Variables contain values. For example, the variable myName is assigned the string "Dori". Another way to write this is myName="Dori" . The equals sign can be read as "is set to." In other words, the variable myName now contains the value "Dori". Tips -
JavaScript is case sensitive. This means that myname is not the same as myName , and neither is the same as MyName . -
Variable names cannot contain spaces or other punctuation, or start with a digit. They also can't be one of the JavaScript reserved words. See Appendix B for a list of JavaScript reserved words. Operators Operators are the symbols used to work with variables. You're already familiar with operators from simple arithmetic; plus and minus are operators. See Table 1.3 for the full list of operators. Table 1.3. Operators Operator | What It Does | x + y (Numeric) | Adds x and y together | x + y (String) | Concatenates x and y together | x - y | Subtracts y from x | x * y | Multiplies x and y together | x / y | Divides x by y | x % y | Modulus of x and y (i.e., the remainder when x is divided by y) | x++, ++ x | Adds one to x (same as x = x + 1) | x--, --x | Subtracts one from x (same as x = x - 1) | -x | Reverses the sign on x | Tips -
While both x++ and ++x add one to x, they are not identical; the former increments x after the assignment is complete, and the latter before. For example, if x is 5, y=x++ results in y set to 5 and x set to 6, while y=++x results in both x and y set to 6. The operator - (minus sign) works similarly. -
If you mix numeric and string values when adding two values together, the result is a string. For example, cat + 5 results in cat5 . |