if statement
In .js
files, you can use if
statements in the following formats:
if (expression) statement
: whenexpression
is truthy, executestatement
.if (expression) statement1 else statement2
: whenexpression
is truthy, executestatement1
. Otherwise, executestatement2
.if ... else if ... else statementN
With this format of if statement, a statement amongstatement1
~statementN
can be selected to execute.
Syntax example:
// if ...
if (expression) statement;
if (expression)
statement;
if (expression) {
code block;
}
// if ... else
if (expression) statement;
else statement;
if (expression)
statement;
else
statement;
if (expression) {
code block;
} else {
code block;
}
// if ... else if ... else ...
if (expression) {
code block;
} else if (expression) {
code block;
} else if (expression) {
code block;
} else {
code block;
}
switch statement
- The
default
branch can be omitted. - Only
variable
,number
, andstring
can follow thecase
keyword.
Syntax example:
switch (expression) {
case variable:
statement;
case number:
statement;
break;
case string:
statement;
default:
statement;
}
Code sample:
var exp = 10;
switch ( exp ) {
case "10":
console.log("string 10");
break;
case 10:
console.log("number 10");
break;
case exp:
console.log("var exp");
break;
default:
console.log("default");
}
Output:
number 10
for statement
Supports the use of break
and continue
keywords.
Syntax example:
for (statement; statement; statement)
statement;
for (statement; statement; statement) {
code block;
}
Code sample:
for (var i = 0; i < 3; ++i) {
console.log(i);
if( i >= 1) break;
}
Output:
0
1
while statement
- When
expression
is true, loop through thestatement
orcode block
. - Supports the use of
break
andcontinue
keywords.
Syntax example:
while (expression)
statement;
while (expression){
code block;
}
do {
code block;
} while (expression)