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Questions and Answers
The syntax of ES5 allowed for something called implicit ______, which have been the source of many frustrating programming errors.
globals
JavaScript introduced the concept of ______ mode, which would prevent implicit globals.
strict
Strict mode is enabled with the string 'use ______' on a line by itself, before any other code.
strict
If you do this in global scope, the entire script will execute in ______ mode, and if you do it in a function, the function will execute in ______ mode.
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Because ______ mode applies to the entire script if used in the global scope, you should use it with caution.
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If you don’t want to enable ______ mode in every single function you write, you can wrap all of your code in one function that’s executed immediately.
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Understanding ______ is an important part of learning any programming language.
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To learn more about what ______ mode does, see the MDN article on ______ mode.
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Study Notes
Strict Mode
- Implicit globals in ES5 allowed JavaScript to assume undeclared variables as global, leading to errors.
- Strict mode prevents implicit globals and is enabled with the string "use strict" on a line by itself.
- If used in global scope, strict mode applies to the entire script, while in a function, it only applies to that function.
- Enabling strict mode in global scope can affect other scripts, so it's generally inadvisable.
- Wrapping code in an immediately invoked function can enable strict mode without affecting other scripts.
Benefits of Strict Mode
- Strict mode is considered a good thing and can help prevent errors.
- Linters can also help prevent errors, but using strict mode can provide extra protection.
Scope and Closures
- Understanding scope is essential in programming languages.
- The introduction of let brings JavaScript in line with other modern languages.
- JavaScript is one of the first popular languages to support closures.
- Closures are an important part of modern JavaScript development and have been used effectively by the JavaScript community.
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Description
Learn about JavaScript's strict mode, its importance in preventing implicit globals, and the benefits of using it in coding.
