JS Basic Learning 3

1. Control statements

(1) If control statement

If-else basic format if (expression) {statement 1; ...} else{statement 2; ...} Function description if the value of the expression is true Then statement 1 is executed, otherwise the statement 2 is executed

if (0>2) {
    Console.log ("success!")
}else{
    Console.log ("Failure")
}
>>

Failure

　

(2) switch Select control statement

Switch basic format switch (expression) {case    value 1: statement 1;break;    Case value 2: statement 2;break;    Case Value 3: statement 3;break;    Default: statement 4;}

x=2;
Switch (x) {
    Case 0:console.log ("Sunday");
    Case 1:console.log ("Monday");
    Case 2:console.log ("Tuesday");
    Case 3:console.log ("Wednesday");
    Case 4:console.log ("Thursday");
    Case 5:console.log ("Friday");
    Case 6:console.log ("Saturday");
    Default:console.log ("undefined");
}
>>
Tuesday

　　

(3) For loop control statement

For loop basic format for (initialize; condition; increment) {statement 1; ...} The function description realizes the condition loop, when the condition is established, executes the statement 1, otherwise jumps out the loop body

for (Var i=0;i<10;i++) {
    document.write ("}
>>

Hello0hello1hello2hello3hello4hello5hello6hello7hello8hello9

　　

(4) While loop control statement

While loop basic format while (condition) {statement 1; ...} Function description run function and for similar, when the condition is formed loop execution statement curly braces {} Inside the statement, otherwise jump out of the loop

var i=0;
while (I<10) {
    document.write ("    i++;
}
>>

Hello0hello1hello2hello3hello4hello5hello6hello7hello8hello9

　　

2. Exception handling

try {    //This piece of code runs from top to bottom, where any one of the statements throws an exception the code block ends running}catch (e) {    ///If an exception is thrown in a try code block, the code in the catch code block is executed.    //e is a local variable that is used to point to an Error object or other thrown object}finally {//Whether or not the code in the     try is thrown (even if there is a return statement in the try code block), the finally code block is always executed. }

(1) Normally, no exception is run        try {            console.log ("Hello") that does not trigger the catch;        }        catch (e) {            console.log (e);        }        finally {            Console.log ("finally");        } >>hellofinally (2) An exception is detected when an unknown element x appears in the following code, and the run of the catch is triggered after the try has run out of print hello.        try {            console.log ("Hello");                Console.log (x);        }        catch (e) {            console.log (e);        }        finally {            Console.log ("finally");        } >>HELLOREFERENCEERROR:X is not definedfinally

　　

JS Basic Learning 3