JavaScript common statements loop, judgment, string to number

1. switch

Select one of multiple code blocks to be executed

switch(e) {
     case 1:
        //e is 1, execute break here;
     case 2:
        //e is 2, execute break here;
     default:
        // None of them meet the requirements to execute here} 

Notice:

• It is not necessary to use break to interrupt the last case in switch code block. The code block ends naturally here.
• Switch case uses strict comparison (===), the value must be of the same type to be matched.
• If JavaScript encounters the break keyword, it will jump out of the switch code block, so the system will not continue to execute, which can improve performance.
  

2. While Loop

If the following condition is not met, the loop will continue until the parameter "i" is not less than 10

while (i < 10) {
    text += "The number is" + i;
    i++;
}

3. Do/While Loop

This is similar to the above, but it will be executed at least once, because it is executed first and then judged.

do {
    text += "The number is " + i;
    i++;
 }
while (i < 10);

• for - loop executes a block of code a specified number of times.
• for/in - loop through the properties of an object
• while - loops through a specified block of code while a specified condition is true
• do/while - Also loops through a specified block of code while a specified condition is true, but the loop executes the block of code once before evaluating the condition
  

3. Convert string to number

Many students will encounter the problem of converting strings to numbers, but they can't remember the words to convert, or they are too lazy to write them. In this case, just add a + sign in front of the variable.

Like this:

let a = "12" // This is a string console.log(+a) // Now it is converted to the number 12

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