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The key to understanding design patterns such as IIFE is to realize that prior to ES6, JavaScript only featured function scope (thus lacking block scope), passing values by reference inside closures. [9] This is no longer the case, as the ES6 version of JavaScript implements block scoping using the new let and const keywords. [10]
In other languages, such as Python, a name's scope begins at the start of the relevant block where the name is declared (such as the start of a function), regardless of where it is defined, so all names within a given block have the same scope. In JavaScript, the scope of a name declared with let or const begins at the name declaration, and the ...
Pointers to block and block literals are marked with ^. Normal local variables are captured by value when the block is created, and are read-only inside the block. Variables to be captured by reference are marked with __block. Blocks that need to persist outside of the scope they are created in may need to be copied. [20] [21]
Declaring a variable (with the keyword var) in the global scope (i.e. outside of any function body (or block in the case of let/const)), assigning a never declared identifier or adding a property to the global object (usually window) will also create a new global variable.
In computer programming, a block or code block or block of code is a lexical structure of source code which is grouped together. Blocks consist of one or more declarations and statements . A programming language that permits the creation of blocks, including blocks nested within other blocks, is called a block-structured programming language .
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In computer programming, variable shadowing occurs when a variable declared within a certain scope (decision block, method, or inner class) has the same name as a variable declared in an outer scope. At the level of identifiers (names, rather than variables), this is known as name masking.
A block is a grouping of code that is treated collectively. Many block syntaxes can consist of any number of items (statements, expressions or other units of code) – including one or zero. Languages delimit a block in a variety of ways – some via marking text and others by relative formatting such as levels of indentation.