# Code Style

Rules which enforce a specific coding style.
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## AssignmentInOperand

Since: PMD 5.0

Priority: Medium High (2)

Avoid assignments in operands; this can make code more complicated and harder to read. This is sometime indicative of the bug where the assignment operator ‘=’ was used instead of the equality operator ‘==’.

This rule is defined by the following XPath expression:

    //IfStatement[$allowIf = false()]/child::node()[1]/descendant-or-self::node()[self::Assignment or self::UnaryExpression[$allowIncrementDecrement = false() and (@Image = "--" or @Image = "++")]]
    |
        //WhileLoop[$allowWhile = false()]/child::node()[1]/descendant-or-self::node()[self::Assignment or self::UnaryExpression[$allowIncrementDecrement = false() and (@Image = "--" or @Image = "++")]]
    |
        //DoLoop[$allowWhile = false()]/child::node()[2]/descendant-or-self::node()[self::Assignment or self::UnaryExpression[$allowIncrementDecrement = false() and (@Image = "--" or @Image = "++")]]
    |
        //ForLoop[$allowFor = false()]/child::node()[2]/descendant-or-self::node()[self::Assignment or self::UnaryExpression[$allowIncrementDecrement = false() and (@Image = "--" or @Image = "++")]]
    |
       //ConditionalExpression[$allowTernary = false()]/child::node()[1]/descendant-or-self::node()[self::Assignment or self::UnaryExpression[$allowIncrementDecrement = false() and (@Image = "--" or @Image = "++")]]
    |
       //ConditionalExpression[$allowTernaryResults = false()]/child::node()[position() = 2 or position() = 3]/descendant-or-self::node()[self::Assignment or self::UnaryExpression[$allowIncrementDecrement = false() and (@Image = "--" or @Image = "++")]]

Example(s):

    var x = 2;
    // Bad
    if ((x = getX()) == 3) {
        alert('3!');
    }

    function getX() {
        return 3;
    }

This rule has the following properties:

Name | Default Value | Description | Multivalued
--- | --- | --- | ---
allowIf | false | Allow assignment within the conditional expression of an if statement | no
allowFor | false | Allow assignment within the conditional expression of a for statement | no
allowWhile | false | Allow assignment within the conditional expression of a while statement | no
allowTernary | false | Allow assignment within the conditional expression of a ternary operator | no
allowTernaryResults | false | Allow assignment within the result expressions of a ternary operator | no
allowIncrementDecrement | false | Allow increment or decrement operators within the conditional expression of an if, for, or while statement | no

Use this rule with the default properties by just referencing it:

    <rule ref="category/ecmascript/codestyle.xml/AssignmentInOperand" />

Use this rule and customize it:

    <rule ref="category/ecmascript/codestyle.xml/AssignmentInOperand">
        <properties>
            <property name="allowIf" value="false" />
            <property name="allowFor" value="false" />
            <property name="allowWhile" value="false" />
            <property name="allowTernary" value="false" />
            <property name="allowTernaryResults" value="false" />
            <property name="allowIncrementDecrement" value="false" />
        </properties>
    </rule>

## ForLoopsMustUseBraces

Since: PMD 5.0

Priority: Medium (3)

Avoid using ‘for’ statements without using curly braces.

This rule is defined by the following XPath expression:

    //ForLoop[not(child::Scope)]
    |
    //ForInLoop[not(child::Scope)]

Example(s):

    // Ok
    for (var i = 0; i < 42; i++) {
        foo();
    }

    // Bad
    for (var i = 0; i < 42; i++)
        foo();

Use this rule by referencing it:

    <rule ref="category/ecmascript/codestyle.xml/ForLoopsMustUseBraces" />

## IfElseStmtsMustUseBraces

Since: PMD 5.0

Priority: Medium (3)

Avoid using if..else statements without using curly braces.

This rule is defined by the following XPath expression:

    //ExpressionStatement[parent::IfStatement[@Else = true()]]
       [not(child::Scope)]
       [not(child::IfStatement)]

Example(s):

    // Ok
    if (foo) {
        x++;
    } else {
        y++;
    }

    // Bad
    if (foo)
        x++;
    else
        y++;

Use this rule by referencing it:

    <rule ref="category/ecmascript/codestyle.xml/IfElseStmtsMustUseBraces" />

## IfStmtsMustUseBraces

Since: PMD 5.0

Priority: Medium (3)

Avoid using if statements without using curly braces.

This rule is defined by the following XPath expression:

    //IfStatement[@Else = false() and not(child::Scope)]

Example(s):

    // Ok
    if (foo) {
        x++;
    }

    // Bad
    if (foo)
        x++;

Use this rule by referencing it:

    <rule ref="category/ecmascript/codestyle.xml/IfStmtsMustUseBraces" />

## NoElseReturn

Since: PMD 5.5.0

Priority: Medium (3)

The else block in a if-else-construct is unnecessary if the `if` block contains a return. Then the content of the else block can be put outside.

See also: http://eslint.org/docs/rules/no-else-return

This rule is defined by the following XPath expression:

    //IfStatement[@Else=true()][Scope[1]/ReturnStatement]

Example(s):

    // Bad:
    if (x) {
        return y;
    } else {
        return z;
    }

    // Good:
    if (x) {
        return y;
    }
    return z;

Use this rule by referencing it:

    <rule ref="category/ecmascript/codestyle.xml/NoElseReturn" />

## UnnecessaryBlock

Since: PMD 5.0

Priority: Medium (3)

An unnecessary Block is present. Such Blocks are often used in other languages to introduce a new variable scope. Blocks do not behave like this in ECMAScipt, and using them can be misleading. Considering removing this unnecessary Block.

This rule is defined by the following XPath expression:

    //Block[not(parent::FunctionNode or parent::IfStatement or parent::ForLoop or parent::ForInLoop
        or parent::WhileLoop or parent::DoLoop or parent::TryStatement or parent::CatchClause)]
    |
    //Scope[not(parent::FunctionNode or parent::IfStatement or parent::ForLoop or parent::ForInLoop
        or parent::WhileLoop or parent::DoLoop or parent::TryStatement or parent::CatchClause)]

Example(s):

    if (foo) {
        // Ok
    }
    if (bar) {
        {
            // Bad
        }
    }

Use this rule by referencing it:

    <rule ref="category/ecmascript/codestyle.xml/UnnecessaryBlock" />

## UnnecessaryParentheses

Since: PMD 5.0

Priority: Medium Low (4)

Unnecessary parentheses should be removed.

This rule is defined by the following XPath expression:

    //ParenthesizedExpression/ParenthesizedExpression

Example(s):

    var x = 1; // Ok
    var y = (1 + 1); // Ok
    var z = ((1 + 1)); // Bad

Use this rule by referencing it:

    <rule ref="category/ecmascript/codestyle.xml/UnnecessaryParentheses" />

## UnreachableCode

Since: PMD 5.0

Priority: High (1)

A ‘return’, ‘break’, ‘continue’, or ‘throw’ statement should be the last in a block. Statements after these will never execute. This is a bug, or extremely poor style.

This rule is defined by the following XPath expression:

    //ReturnStatement[following-sibling::node()]
    |
        //ContinueStatement[following-sibling::node()]
    |
        //BreakStatement[following-sibling::node()]
    |
        //ThrowStatement[following-sibling::node()]

Example(s):

    // Ok
    function foo() {
       return 1;
    }
    // Bad
    function bar() {
       var x = 1;
       return x;
       x = 2;
    }

Use this rule by referencing it:

    <rule ref="category/ecmascript/codestyle.xml/UnreachableCode" />

## WhileLoopsMustUseBraces

Since: PMD 5.0

Priority: Medium (3)

Avoid using ‘while’ statements without using curly braces.

This rule is defined by the following XPath expression:

    //WhileLoop[not(child::Scope)]

Example(s):

    // Ok
    while (true) {
        x++;
    }

    // Bad
    while (true)
        x++;

Use this rule by referencing it:

    <rule ref="category/ecmascript/codestyle.xml/WhileLoopsMustUseBraces" />