JavaScript "2"

Condition Judgment:

Use if () {}else{} in JavaScript to determine

If the statement block contains only one statement, you can omit {}:

var age=20;

if (age>=18)

Alert ("You are an adult")

Else

Alert ("You haven't grown up, baby")

Suggested write {}

Multi-line condition judgment: if () {

}else if () {

}else{

}

Cycle:

To calculate the value we can write the expression directly 1+2+3//6

To calculate 1+2+3+4+5+......+10 can barely write it down

But to calculate 1+2+3+.....+10000, it's impossible to write the expression directly.

In order for the computer to compute thousands of repetitive operations, we need to loop the statement:

There are two types of JavaScript loops, one for loops, and the execution of statements by looping, ending conditions, and incrementing conditions:

var x=0;

var i;

for (i=1;i<=10000;i++) {

X=x+1

}

Control conditions for the FOR loop:

I=1 This is the initial value assigns the variable I to a value of 1

i<=10000 This is the judging condition, the loop continues when it is satisfied, and exits when it is not satisfied.

i++ This is the increment condition after each loop, because the variable i is incremented by 1 after each cycle, so he will eventually exit the loop after several cycles without satisfying the condition i<10000

The most common place for a for loop is to iterate through an array using an index:

var arr=["Apple", "Banana", "Orange"]

var i, X;

for (i=0;i<arr.length;i++) {

X=arr[i]

Console.log (x)

}

Shorthand:

var arr=["Apple", "Banana", "Orange"]

for (Var i=0;i<arr.length;i++) {

X=arr[i]

Console.log (x)

}

　　　　

for3 Conditions of the loop can be omitted, if there is no Exit loop judgment condition, you must use break the statement to exit the loop, or the dead loop:

0;for (;;) { // 将无限循环下去    if (x > 100) { break; // 通过if判断来退出循环 } x ++;}

JavaScript "2"