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Strict Mode
ECMAScript 5 was the first to introduce the concept of strict mode. Strict mode allows you to opt-in to stricter checking for JavaScript error conditions either globally or locally within a single function. The advantage of strict mode is that you'll be informed of errors earlier, so some of the ECMAScript quirks that cause programming errors will be caught immediately.
The rules of strict mode are important to understand, as future versions of ECMAScript will mandate the increasingly pervasive use of strict mode. Strict mode is supported in all major browsers.
