JavaScriptCore

You can execute JavaScript code within a context by calling the evaluateScript(_:) method on a JSContext object. evaluateScript(_:) returns a JSValue object containing the value of the last expression that was evaluated. For example, a JavaScript expression that adds the numbers 1, 2, and 3 results in the number value 6.

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The article explores the JavaScriptCore framework, which integrates WebKit’s JavaScript engine into Swift apps, allowing developers to execute JavaScript code and interoperate with Swift.

Using JSContext, developers can evaluate scripts with evaluateScript(_:), returning JSValue objects convertible to Swift types like String, Bool, or Int32 via methods like toInt32(). JavaScript variables and functions persist in the context, accessible via objectForKeyedSubscript(_:), while Swift values and Objective-C blocks can be set with setObject(_:forKeyedSubscript:).

The JSExport protocol enables direct mapping of Swift classes to JavaScript, though it requires significant setup with @objc protocols and dynamic properties. The article demonstrates practical applications, such as parsing JSON to create Swift objects and rendering Mustache templates, emphasizing error handling with exceptionHandler and improved debugging via evaluateScript(_:withSourceURL:).

Swift’s type safety and clear syntax enhance JavaScriptCore’s usability, making it a powerful tool for leveraging JavaScript’s ecosystem in iOS and macOS apps, from scripting to cross-platform feature parity.