Statement

if statement

In .js files, you can use if statements in the following formats:

• if (expression) statement: when expression is truthy, execute statement.
• if (expression) statement1 else statement2: when expression is truthy, execute statement1. Otherwise, execute statement2.
• if ... else if ... else statementN With this format of if statement, a statement among statement1 ~ 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, and string can follow the case 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 the statement or code block.
• Supports the use of break and continue keywords.

Syntax example:

while (expression)
  statement;

while (expression){
  code block;
}

do {
  code block;
} while (expression)