• for statement
• do while
• while
• labeled statement
• break statement
• continue statement
  • Example
• for…in statement
• for…of statement
  • The difference of for … of and for … in

Loops offer a quick and easy way to do something repeatedly.

for statement

do while

while

labeled statement

A label provides a statement with an identifier that lets you refer to it elsewhere in your program(引用到别的位置).

The syntax:

label :
   statement

For example, you can use a label to identify a loop, and then use the break or continue statements to indicate whether a program should interrupt the loop or continue its execution.

markLoop:
while (theMark == true) {
   doSomething();
}

The label markloop identifies a while loop.

break statement

Use the break statement to terminate a loop, switch, or in conjunction with (链接到) a labeled statement.

The syntax：

break;
break label;

The first form of the syntax terminates the innermost(最内层) enclosing loop or switch; the second form of the syntax terminates the specified enclosing labeled statement.

continue statement

The continue statement can be used to restart a while, do-while, for, or label statement.

The syntax：

continue;
continue label;

Example

checkiandj:
  while (i < 4) {
    console.log(i);
    i += 1;
    checkj:
      while (j > 4) {
        console.log(j);
        j -= 1;
        if ((j % 2) == 0) {
          continue checkj;
        }
        console.log(j + ' is odd.');
      }
      console.log('i = ' + i);
      console.log('j = ' + j);
  }

A statement labeled checkiandj contains a statement labeled checkj. If continue is encountered, the program terminates the current iteration of checkj and begins the next iteration.

If continue had a label of checkiandj, the program would continue at the top of the checkiandj statement.(如果continue只有一个label标记，就会从标记循环语句的上面的代码执行)

for…in statement

The for...in statement iterates a specified variable over all the enumerable properties(可枚举的属性) of an object.

The syntax：

for (variable in object){
    statement;
}

for…of statement

The for...of statement creates a loop Iterating over iterable objects (including Array, Map, Set, arguments object and so on), invoking a custom iteration hook with statements to be executed for the value of each distinct property (对值的每一个独特的属性调用一个将被执行的自定义的和语句挂钩的迭代).

for (variable of object){
    statement;
}

The difference of for … of and for … in

let arr = [3, 5, 7];
arr.foo = 'hello';

for (let i in arr) {
   console.log(i); // logs "0", "1", "2", "foo"
}

for (let i of arr) {
   console.log(i); // logs 3, 5, 7
}
}

While for...in iterates over property names(属性名), `for…of iterates over property values(属性值).