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    if...else

     

    Summary

    Executes a statement if a specified condition is true. If the condition is false, another statement can be executed.

    Version Information

    Statement
    Implemented in: JavaScript 1.0, NES 2.0
    ECMA Version: ECMA-262

    Syntax

    if (condition)
       statement1
    [else
       statement2]
    

    Parameters

    condition
    An expression that evaluates to true or false.
    statement1
    Statement that is executed if condition evaluates to true. Can be any statement, including further nested if statements. To execute multiple statements, use a block statement ({ ... }) to group those statements.
    statement2
    Statement that is executed if condition evaluates to false and the else clause exists. Can be any statement, including block statements and further nested if statements.

    Description

    Multiple if...else statements can be nested to create an else if clause:

    if (condition1)
       statement1
    else if (condition2)
       statement2
    else if (condition3)
       statement3
    ...
    else
       statementN
    

    To see how this works, this is how it would look like if the nesting were properly indented:

    if (condition1)
       statement1
    else
       if (condition2)
          statement2
       else
          if (condition3)
    ...
    

    To execute multiple statements within a clause, use a block statement ({ ... }) to group those statements. In general, it is a good practice to always use block statements, especially in code involving nested if statements:

    if (condition) {
       statements1
    } else {
       statements2
    }
    

    Do not confuse the primitive boolean values true and false with the true and false values of the Boolean object. Any value that is not undefined, null, 0, NaN, or the empty string (""), and any object, including a Boolean object whose value is false, evaluates to true when passed to a conditional statement. For example:

    var b = new Boolean(false);
    if (b) // this condition evaluates to true
    

    Examples

    Example: Using if...else

    if (cipher_char === from_char) {
       result = result + to_char;
       x++;
    } else {
       result = result + clear_char;
    }
    

    Example: Assignment within the conditional expression

    It is advisable to not use simple assignments in a conditional expression, because the assignment can be confused with equality when glancing over the code. For example, do not use the following code:

    if (x = y) {
       /* do the right thing */
    }
    

    If you need to use an assignment in a conditional expression, a common practice is to put additional parentheses around the assignment. For example:

    if ((x = y)) {
       /* do the right thing */
    }
    

     

     

    Document Tags and Contributors

    Contributors to this page: Sevenspade
    Last updated by: Sevenspade,