js Tag Syntax Usage Details
- 2021-11-29 05:52:24
- OfStack
Foreword:
We often use recursion in daily development,
break
,
continue
,
return
Wait for the statement to change the position where the program runs, in fact, in the
JavaScript
Label statements are also provided to mark the specified block of code for jumping to the specified location. This article records how to use the label statement under 1.
1. Introduction to tag statements
A label statement is used to label a statement. The label can have the same name as a variable. It is an independent syntax element (neither a variable nor a type), and its function is to identify the "tagged statement (
labeled statement
) "is equivalent to a locator for jumping to anywhere in the program, with the following syntax:
label: statement
For example:
hello:console.log("hello")
Label statements can change the execution flow of programs, similar to
break
,
continue
And
return
. Among them
break
And
continue
It can be used with tag 1.
2. The tag statement uses the
(1) The tag statement is used in conjunction with break to jump out of a specific loop
let num = 0;
mylabel:
for (let i = 0; i < 10; i++) {
for (let j = 0; j < 10; j++) {
if (i == 5 && j == 5) {
break mylabel;
}
num++;
}
}
console.log(num); // 55
In this example,
outermost
The label identifies the first
for
Statement. Normally, each loop executes 10 times, which means that
num++
Statement is executed 100 times, and at the end of the loop
console.log
The result should be 100. But,
break
Statement brings 1 variable, which is the label to exit to. Adding tags not only makes
break
Exiting the inner loop (using the variable j) also exits the outer loop (using the variable i). When i and j are both equal to 5, the loop stops executing, and at this time
num
The value of is 55.
(2) Label statements are used in conjunction with continue
let num = 0;
mylabel:
for (let i = 0; i < 10; i++) {
for (let j = 0; j < 10; j++) {
if (i == 5 && j == 5) {
continue mylabel;
}
num++;
}
}
console.log(num); // 95
continue
Statement forces the loop to continue, but not the inner loop, but the outer loop. Executes when i and j are both equal to 5
continue
Skip to the outer loop and continue execution, resulting in less execution of the inner loop by 5 times. As a result,
num
Equal to 95.
Summary:
Combining tag statements with
break
,
continue
It can implement complex logic, but it is also prone to errors. Note that tags should use descriptive text and not be nested too deeply.