Statements

See Language Specification.

if...else

syntax:

if (boolean-expression) [expression-statement | block]
[else expression-statement | block]

e.g.:

if (user_name == 'guest') quit();

or

if (user_name == 'admin') {
    var user = new User();
    user.role = 'admin';
}

Since the expression-statement in else could contains it...else self, so a if...else statement could be repeatedly used:

if (user_role == 'guest') {
    ...
} else if (user_role == 'admin') {
    ...
}

But an ambiguous statement as below is not recommended:

if (a < 5) 
  return 20;
else
  if (b == 10)           // not good sample
    return 30;
  else 
    return 40;

Always use block instead of expression-statement is strongly recommended:

if (a < 5) {
  return 20;
} else {
  if (b == 10) {         // good sample
    return 30;
  } else {
    return 40;
  }
}

for

for statement be used to loop until condition is met. (boolean-expression to be true)

syntax:

for ( [local-]variable-declaration-list?; boolean-expression?; expression-statement-list? ) 
    [expression-statement | block]

e.g.:

var total = 0;

for (var i = 0; i < 10; i++) {
    total += i;
}

console.log(total);

The result is:

45

One or more variables or expression-statements could be used in for statement:

for (var a = 0, b = 1; a < 10 && b < 10; a++, b++) {
    c = a + b;

for...in

for...in used to iterate over an object which must be enumerable. (supported by implements IEnumerable in .Net)

By default the following built-in types in ReoScript could be enumerable:

• Array
• Object
• String

syntax:

for ( [var]? identifier in expression ) [expression-statement | block]

Iterate over array

var arr = [1,5,'ok',false];

for (element in arr) {
    console.log(element);
}

The result is:

1
5
ok
false

Iterate over object

var obj = {name: 'apple', color: 'red', amount: 5};

for (key in obj) {
    console.log(key + ': ' + obj[key]);
}

The result is:

name: apple
color: red
amount: 5

Iterate over string

var str = 'abc';

for (char in str) {
    console.log(char);
}

The result is:

a
b
c

while

syntax:

while (boolean-expression) [expression-statement | block]

e.g.:

var i = 0;
while (i < 10) i++;

or

while (true) {
    console.log('forever');
}

Terminal Statement

The following statements is terminal statement:

break;                // stop and jump out current loop
continue;             // stop but continue current loop from next begin
return expresion?;    // stop and return from current function 

switch

syntax:

switch (expression) {
    [ case expression: 
    | default:
    | expression-statement
    | block ]*
}

e.g.:

var user = get_login_user();

switch (user.role) {
    case 'user':
        console.log('Welcome ' + user.name + '!');
        break;

    case 'admin':
        console.log(get_event_count() + ' event(s).');
        break;

    case 'guest':
        forward('/common/need_login');
        break;

    default:
        console.log('unknown role, system exit.');
        exit();
        break;
}

Code will be continue if no 'break' indicated:

var user = get_login_user();

switch (user.role) {
    case 'user':
        user.remark = 'user';
    case 'admin':
        user.login_time = new Date();
    case 'guest':
        console.log('welcome!');
        break;

    default:
        console.log('unknown role, system exit.');
        exit();
        break;
}

try...catch...finally

See Error handling.

See Also

• [Language Specification](Language Specification)
• Variables
• Functions
• Prototypes