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    block

    Summary

    A block statement (or compound statement in other languages) is used to group zero or more statements. The block is delimited by a pair of curly brackets.

    Syntax

    {
      statement_1;
      statement_2;
      ...
      statement_n;
    }
    
    statement_1, statement_2, statement_n
    Statements grouped within the block statement.

    Description

    This statement is commonly used with control flow statements (e.g. if, for, while). For example:

    while (x < 10) {
      x++;
    }
    

    Note that the block statement does not end with a semicolon.

    The block statement is often called compound statement in other languages. It allows you to use multiple statements where JavaScript expects only one statement. Combining statements into blocks is a common practice in JavaScript. The opposite behavior is possible using an empty statement, where you provide no statement, although one is required.

    No block scope

    Important: Variables declared with var do not have block scope. Variables introduced with a block are scoped to the containing function or script, and the effects of setting them persist beyond the block itself. In other words, block statements do not introduce a scope. Although "standalone" blocks are valid syntax, you do not want to use standalone blocks in JavaScript, because they don't do what you think they do, if you think they do anything like such blocks in C or Java. For example:

    var x = 1;
    {
      var x = 2;
    }
    console.log(x); // logs 2
    

    This logs 2 because the var x statement within the block is in the same scope as the var x statement before the block. In C or Java, the equivalent code would have outputted 1.

    Specifications

    Specification Status Comment
    ECMAScript 1st Edition. Standard Initial definition. Implemented in JavaScript 1.0
    ECMAScript 5.1 (ECMA-262)
    The definition of 'Block statement' in that specification.
    Standard  
    ECMAScript 6 (ECMA-262)
    The definition of 'Block statement' in that specification.
    Draft  

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

    See also

    Document Tags and Contributors

    Last updated by: fscholz,
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