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JavaScript syntax
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Native functions and methods

eval (expression)

Evaluates the first parameter as an expression, which can include
assignment statements. Variables local to functions can be referenced by
the expression. However, eval represents a major security risk, as it
allows a bad actor to execute arbitrary code, so its use is
discouraged.cite-ref-deve-eval-27-0[27]

> (function foo() {
... var x = 7;
... console.log("val " + eval("x + 2"));
... })();
val 9
undefined

See also

• Comparison of JavaScript-based source code editors
• JavaScript

References

cite-note-11. ↑ "JavaScript 1.1 specification". Archived from the original on 26 February 2017. Retrieved 19 April 2006.
cite-note-22. ↑ "Chapter 1. Basic JavaScript". speakingjs.com. Archived from the original on 10 February 2022. Retrieved 22 September 2020.
cite-note-33. ↑ citerefflanagan2006Flanagan, David (2006). JavaScript: The definitive Guide. "O'Reilly Media, Inc.". p. 16. ISBN 978-0-596-10199-2. Omitting semicolons is not a good programming practice; you should get into the habit of inserting them.
cite-note-44. ↑ citereffariasFarias, Bradley. "Hashbang Grammar". GitHub. Retrieved 13 July 2025.
cite-note-55. ↑ "Storing the information you need — Variables - Learn web development | MDN". developer.mozilla.org. 9 May 2023. Retrieved 23 June 2023.
cite-note-66. ↑ "Values, Variables, and Literals - MDC". Mozilla Developer Network. 16 September 2010. Archived from the original on 29 June 2011. Retrieved 1 February 2020.
cite-note-77. ↑ "JavaScript Hoisting". W3Schools. Archived from the original on 31 March 2022. Retrieved 17 December 2021. In JavaScript, a variable can be declared after it has been used. In other words; a variable can be used before it has been declared.
cite-note-88. ↑ "JavaScript Scoping and Hoisting Archived 8 May 2021 at the Wayback Machine", Ben Cherry Archived 28 February 2021 at the Wayback Machine, Adequately Good Archived 8 March 2022 at the Wayback Machine, 8 February 2010
cite-note-99. ↑ ECMA-262 5e edition clarified this behavior with the Declarative Environment Record and Object Environment Record. With this formalism, the global object is the Object Environment Record of the global Lexical Environment (the global scope).

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