JavaScript In Practice: ES6 And Beyond/

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Defining Proxies

Defining Proxies

solve fundamental operations (like property lookup, assignment, enumeration, function invocation, etc.) using proxies

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We can create a proxy in the following way:

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let proxy = new Proxy( target, trapObject );

The first argument is target representing the proxied constructor function, class, or object.
The second argument is an object containing traps that are executed once the proxy is used in a specific way.
Let’s put our knowledge into practice by proxying the following target:

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class Student {
    constructor(first, last, scores) {
        this.firstName = first;
        this.lastName = last;
        this.testScores = scores;
    }
    get average() {
        let average = this.testScores.reduce( 
            (a,b) => a + b, 
            0 
        ) / this.testScores.length;
        return average;
    }
}
let john = new Student( 'John', 'Dwan', [60, 80, 80] );
console.log(john);

We will now define a proxy on the target object john:

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let johnProxy = new Proxy( john, {
    get: function( target, key, context ) {
        console.log( `john[${key}] was accessed.` );
        // return undefined;
    } 
});

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