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This article mainly explains "how to use the basic cycle of Javascript". The content of the explanation is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "how to use the basic cycle of Javascript".

Cyclic for

A loop is that any language will have a command to execute a piece of code repeatedly.

For example, loop the code block 5 times:

For (let I = 0; I < 5; iTunes +) {let text = `The current number is ${I} `console.log (text)}

/ / output result:

The current number is 0

The current number is 1

The current number is 2

The current number is 3

The current number is 4

In this example, let I = 0 is the count variable that declares the loop, I < 5 is the condition for the end of the loop, iSum + is the update step of the count variable, and all the code in {} is the code block inside the loop.

The specific process is as follows: the counting variable performs the termination condition judgment operation, if the result is true, the loop body executes, and the step size update operation is performed after the end, so as to get a new result to participate in the judgment again; if the result is false, the cycle is terminated immediately

So if you want to control the number of loops, you can usually change the realization of the judgment condition, and if the loop condition is always true, it is an endless loop.

For-in

For-in loops are special loops that can be used to loop objects or arrays (usually circular arrays, using for-of)

Let o = {name: 'dapiaoliang', age: 18, sex:' woman'} / / output all key-value pairs in the object in a loop. You can use for-infor (let key in o) {let text = `current attribute name: ${key}, value: ${o [key]}`}

/ / result (the output order of this loop may be different, but the number will not change)

Current attribute name: name, value: dapiaoliang

Current attribute name: age, value: 18

Current attribute name: sex, value: woman

Thus, for-in is used to loop through all key-value pairs within an object, and the specific output order may change, but each key-value pair will be looped once.

For-of

For-of is a loop command dedicated to a circular array or similar array structure (Iterator interface)

Let arr = ["dapiaoliang", 18, 'woman'] for (let value of arr) {let text = `The current value is: ${value} `console.log (text)}

/ / result

The current value is: dapiaoliang

The current value is: 18

The current value is: woman

Similar to for-in, each item of data in an array can be looped directly

While

While is a variant of for. (not commonly used)

While (conditional) {loop body}

When the condition is true, the loop body executes. The loop has no count variable and does not need to update the step size. So the condition usually needs to be a variable parameter, and if it is not a variable parameter, it needs to have a definite termination condition in the loop body.

Do-while

Do-while is a special while loop (not commonly used)

Do {Loop body} while (condition)

The current number is 0

The current number is 1

The current number is 2

The current number is 4

It seems that the conditions of the while and the loop body have been exchanged, so the loop body, at the first time, will be executed without judging the condition. After the execution is finished, the judgment will be made, and the result of the judgment will determine whether the loop will be repeated next time.

So, the condition of do-while is to decide whether to loop next time, and the first time will always be executed, so it can be understood as a while loop executed at least once.

Jump out of the cycle

If you need to jump out of the loop within the code block for some reason, you can use the corresponding keyword.

Break is used to permanently terminate this loop, and continue is used to end the current loop (immediately move on to the next one)

For example, skip the case of I = 3

For (let I = 0; I < 5; iTunes +) {if (I = 3) {continue} let text = `The current number is ${I} `console.log (text)}

In the above example, if the loop body is judged to be true and the continue is executed, the next two lines of code will not be executed this time and will immediately move on to the next loop.

For (let I = 0; I < 5; iTunes +) {if (I = 3) {break} let text = `The current number is ${I} `console.log (text)}

The current number is 0

The current number is 1

The current number is 2

At this point, the inner judgment is break, so when break is executed in iTune3, then all subsequent cycles will not be executed. Break shuts down the entire loop.

Thank you for your reading, the above is the content of "how to use Javascript basic cycle". After the study of this article, I believe you have a deeper understanding of how to use Javascript basic cycle, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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