Loops
To understand conditional statements, we imagined the JavaScript
interpreter following a branching path through your source code. The
looping statements are those that bend that path
back upon itself to repeat portions of your code. JavaScript has four
looping statements: while, do/while, for, and for/in. The subsections below explain each
in turn. One common use for loops is to iterate over the elements of
an array. Iterating Arrays discusses this kind of
loop in detail and covers special looping methods defined by the Array
class.
while
Just as the if statement is
JavaScript’s basic conditional, the while statement is JavaScript’s basic
loop. It has the following syntax:
while(expression)statement
To execute a while
statement, the interpreter first evaluates
expression. If the value of the
expression is falsy, then the interpreter skips over the
statement that serves as the loop body
and moves on to the next statement in the program. If, on the other
hand, the expression is truthy, the
interpreter executes the statement and
repeats, jumping back to the top of the loop and evaluating
expression again. Another way to say this
is that the interpreter executes
statement repeatedly
while the expression
is truthy. Note that you can create an infinite loop with the syntax
while(true).
Usually, you do not want JavaScript to perform exactly the same operation over and over again. In almost every loop, one or more variables change with each iteration of the loop. Since the variables ...
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