Best of Modern JavaScript — Proxy Handlers

Proxy handlers must do what we expect even though we can customize it.

Since 2015, JavaScript has improved immensely.

It’s much more pleasant to use it now than ever.

In this article, we’ll look at how to control JavaScript object operations.

Function Proxy Handlers

We can also add handler methods to the handler we pass into the Proxy constructor or Proxy.revocable method.

apply(target, thisArgument, argumentsList) lets us change the behavior of the apply or call method.

It can also change the behavior of direct calls to a function.

target is the target object which we want to control.

thisArgument lets us pass in the value of this in the function.

argumentsList lets us pass in a list of arguments.

Invariants of Handler Methods

Handler methods have various invariants enforced on them.

They include the following.

apply(target, thisArgument, argumentsList) has no invariants enforced on them.

construct(target, argumentsList, newTarget) must return an object, and not null or a primitive value.

defineProperty(target, propKey, propDesc) must not let us add [properties to an object that isn’t extensible.

The target must have a property must have a non-configurable own property with propKey if configurable is false .

If writable and configurable are both false , then we can’t write a new property to the property.

deleteProperty(target, propKey) can’t delete non-configurable own properties of the target .

get(target, propKey, receiver) must return the property’s value if it has an own, non-writable, and non-configurable data property with name propKey

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Exercise from Eloquent JavaScript. Today, we will write a function that forms a chessboard. You can find the exercise in the Eloquent Javascript book (3rd edition, chapter 2; Program Structure). Write a program that creates a string that represents an 8×8 grid, using newline characters to separate lines. At each position of the grid there is either a space or a “#” character. The characters should form a chessboard.

One of the nice things about learning JavaScript these days is that there is a plethora of choices for writing and running JavaScript code. In this article, I’m going to describe a few of these environments and show you the environment I’ll be using in this series of articles.

To paraphrase the title of an old computer science textbook, “Algorithms + Data = Programs.” The first step in learning a programming language such as JavaScript is to learn what types of data the language can work with. The second step is to learn how to store that data in variables. In this article I’ll discuss the different types of data you can work with in a JavaScript program and how to create and use variables to store and manipulate that data.

Professor JavaScript is a JavaScript online learning courses YouTube Channel. Students can learn how to develop codes with JavaScript from basic to advanced levels through the online courses in this YouTube channel.

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