js语句及语法（JS statements and syntax）.doc

js语句及语法（JS statements and syntax） The statements provided by JavaScript fall into the following categories: 1. variables declaration, assignment statement: var. The syntax is as follows: VAR variable name [= initial value] For example: VAR computer = 32 / / computer definition is a variable, and the initial value is 32. 2. function definition statement: function, return. The syntax is as follows: the function function name (the arguments that the function takes) { Function execution section } The return expression //return statement specifies the value to return. Example: function square (x) { Return x*x } 3. condition and branch statement: if... Else, switch. The if... Else statement completes the branching function of the program flow block: if the condition is established, the program executes the conditional statement or block of statements immediately; otherwise, the program executes the statement or block of statements in else. Syntax is as follows: if (condition) { Execute statement 1 Else{} Execute statement 2 } For example: if (result = true) { Response = you got the right answer! Else{} Response = youre wrong! } Branch statement switch can be handled differently depending on the different values of a variable. The syntax is as follows: switch (expression) { Case label1: statement string 1; Case label2: statement string 2; Case label3: statement string 3; ... Default: statement string 3; } If the value taken by the expression does not match any statement provided in the program, the statement in the default is executed. 4. loop statements: for, for, in, while, break, continue. The syntax of the for statement is as follows: for (initialization section, conditional part, update part) { Executive part... } As long as the condition of the cycle is established, the loop body is repeatedly executed. The for... In statement is a little different from the for statement, which ranges from all attributes of an object or to all elements of an array. The syntax for for