How can 'this' be converted from D3 JavaScript to TypeScript?

Question

How can 'this' be converted from D3 JavaScript to TypeScript?

In JavaScript, 'this' has a different meaning compared to TypeScript, as explained in this informative article 'this' in TypeScript. The JavaScript code below is used to create a thicker stroke on the selected node and give smaller strokes to all other nodes:

node.on('click', function (d) {
   d3.selectAll('circle').attr('stroke-width', 1.5);
   d3.select(this).select('circle').attr('stroke-width', 5);
})

When working with TypeScript, my code looks like this:

this.node.on('click', (d:any) => {
   this.node.selectAll('circle').attr('stroke-width', 1.5);
   [help needed here].select('circle').attr('stroke-width', 5);
}

javascript typescript d3.js arrow-functions lexical-scope

Answer 1

Answer №1

According to information provided in this comment and this answer, the usage of this does not vary significantly between JavaScript and TypeScript.

Your issue stems from attempting to utilize this within an arrow function to access the current DOM element, which is simply ineffective.

The crux of the problem lies in understanding the distinction of this between an arrow function and a regular function, rather than a discrepancy between TypeScript and JavaScript.

Potential Solution

An alternative approach to using this can be found throughout the API: when employing an anonymous function in most D3 methods, the parameters passed are...

... the current datum (d), the current index (i), and the current group (nodes), with this representing the current DOM element (nodes[i]).

Hence, this essentially refers to the current index (the second argument) within the nodes groups (the third argument).

In the given code snippet below:

selection.on("foo", function (d, i, n){
    console.log(this)
    console.log(n[i])
})

Both instances of console.log will yield identical results.

If you are using an arrow function, the recommended solution is (in JavaScript):

this.nodes.on("click", (d, i, n) => {
    d3.select(n[i])//add your remaining code here
})

To further explore utilizing the second and third arguments for accessing the DOM element, refer to this example: d3 v4 retrieve drag DOM target from drag callback when `this` is not available

Answer 2

According to information provided in this comment and this answer, the usage of this does not vary significantly between JavaScript and TypeScript.

Your issue stems from attempting to utilize this within an arrow function to access the current DOM element, which is simply ineffective.

The crux of the problem lies in understanding the distinction of this between an arrow function and a regular function, rather than a discrepancy between TypeScript and JavaScript.

Potential Solution

An alternative approach to using this can be found throughout the API: when employing an anonymous function in most D3 methods, the parameters passed are...

... the current datum (d), the current index (i), and the current group (nodes), with this representing the current DOM element (nodes[i]).

Hence, this essentially refers to the current index (the second argument) within the nodes groups (the third argument).

In the given code snippet below:

selection.on("foo", function (d, i, n){
    console.log(this)
    console.log(n[i])
})

Both instances of console.log will yield identical results.

If you are using an arrow function, the recommended solution is (in JavaScript):

this.nodes.on("click", (d, i, n) => {
    d3.select(n[i])//add your remaining code here
})

To further explore utilizing the second and third arguments for accessing the DOM element, refer to this example: d3 v4 retrieve drag DOM target from drag callback when `this` is not available

Answer 3

Answer №2

The concept presented in this inquiry, Converting 'this' from D3 JavaScript to TypeScript, is misguided. I refrained from downvoting as my intention is to enlighten.

To clarify, the keyword this remains entirely consistent between TypeScript and JavaScript.

All TypeScript syntax that mirrors valid JavaScript syntax possesses identical semantics.

This key aspect distinguishes TypeScript as an expansion of JavaScript.

Addendum: In light of misinterpretation regarding semantic differences, a response shall be appended. The misconception pertains to arrow function syntax.

(params) => expression or block

It is essential to note that => is a feature inherent to JavaScript, not exclusive to TypeScript.

Furthermore, TypeScript naturally accommodates both formats as highlighted above. This implies no translation process is required.

this carries the same connotation in TypeScript as it does in JavaScript.

In both languages, contextual nuances arise when paired with => as opposed to function. Numerous explanations on this subject already exist on SO, hence repetition is unnecessary.

Thus, the solution to this inquiry is presented below:

If working with this script file:

d3-app.js

node.on('click', function (d) {
  d3.selectAll('circle').attr('stroke-width', 1.5);
  d3.select(this).select('circle').attr('stroke-width', 5);
});

Given successful execution, transitioning to TypeScript is desired.

Follow these steps:

Rename d3-app.js to d3-app.ts

That concludes the conversion process.

Answer 4

The concept presented in this inquiry, Converting 'this' from D3 JavaScript to TypeScript, is misguided. I refrained from downvoting as my intention is to enlighten.

To clarify, the keyword this remains entirely consistent between TypeScript and JavaScript.

All TypeScript syntax that mirrors valid JavaScript syntax possesses identical semantics.

This key aspect distinguishes TypeScript as an expansion of JavaScript.

Addendum: In light of misinterpretation regarding semantic differences, a response shall be appended. The misconception pertains to arrow function syntax.

(params) => expression or block

It is essential to note that => is a feature inherent to JavaScript, not exclusive to TypeScript.

Furthermore, TypeScript naturally accommodates both formats as highlighted above. This implies no translation process is required.

this carries the same connotation in TypeScript as it does in JavaScript.

In both languages, contextual nuances arise when paired with => as opposed to function. Numerous explanations on this subject already exist on SO, hence repetition is unnecessary.

Thus, the solution to this inquiry is presented below:

If working with this script file:

d3-app.js

node.on('click', function (d) {
  d3.selectAll('circle').attr('stroke-width', 1.5);
  d3.select(this).select('circle').attr('stroke-width', 5);
});

Given successful execution, transitioning to TypeScript is desired.

Follow these steps:

Rename d3-app.js to d3-app.ts

That concludes the conversion process.

Answer 5

Answer №3

One solution suggested was the substitution of 'this' with 'd3.event.currentTarget'

The revised code snippet reads as follows: d3.select(d3.event.currentTarget).select('circle').attr('stroke-width', 5);

Answer 6

One solution suggested was the substitution of 'this' with 'd3.event.currentTarget'

The revised code snippet reads as follows: d3.select(d3.event.currentTarget).select('circle').attr('stroke-width', 5);

How can 'this' be converted from D3 JavaScript to TypeScript?

Answer №1

Answer №2

Answer №3

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