I am having trouble reaching the _groups attribute in angular/d3js

Question

I am having trouble reaching the _groups attribute in angular/d3js

I am encountering an issue when trying to access the "_groups" property in my code:

function getMouseDate(scale){ 
        var groupElement = d3.select("#group")._groups[0][0]

        var xCoordinate = scale.invert(d3.mouse(groupElement)[0]);

        console.log(xCoordinate);
    }

When I check the console log, I see the following result:

Selection {_groups: Array(1), _parents: Array(1)}
  _groups: Array(1)
    0: Array(1)
      0: g#group

However, compiling the code gives me this error message:

D:/Documents/starter-propre-angular4/src/app/pages/graphe-page/graphe.page.ts (782,32): Property '_groups' does not exist on type 'Selection<BaseType, {}, HTMLElement, any>'.

Therefore, my question is: How can I access the information in "_groups" consistently while working with TypeScript and d3js?

angularjs typescript d3.js

Answer 1

Answer №1

It is important to note that the _groups property, belonging to a Selection object, is meant to be private and should not be accessed directly. In JavaScript, an underscore at the beginning of a member's name typically indicates its privacy. This practice is commonly followed in the language (refer to "Underscore prefix for property and method names in JavaScript").

Because this property is considered private, it is not part of the publicly accessible interface. As a result, it is excluded from the TypeScript type declaration for the d3-selection module, leading to the compiler error you encountered. While the code may function correctly in pure JavaScript, the TypeScript compiler rightly prevents potentially hazardous actions.

However, upon reviewing your code snippet, it is evident that your interest lies more specifically in _groups[0][0], which points to the first node of the selection internally. Fortunately, utilizing the selection.node() method will fetch this initial element accurately. Here is an example of how you can achieve this:

function mouseDate(scale){ 
  var g = d3.select("#group").node();
  var x0 = scale.invert(d3.mouse(g)[0]);
  console.log(x0);
}

Answer 2

It is important to note that the _groups property, belonging to a Selection object, is meant to be private and should not be accessed directly. In JavaScript, an underscore at the beginning of a member's name typically indicates its privacy. This practice is commonly followed in the language (refer to "Underscore prefix for property and method names in JavaScript").

Because this property is considered private, it is not part of the publicly accessible interface. As a result, it is excluded from the TypeScript type declaration for the d3-selection module, leading to the compiler error you encountered. While the code may function correctly in pure JavaScript, the TypeScript compiler rightly prevents potentially hazardous actions.

However, upon reviewing your code snippet, it is evident that your interest lies more specifically in _groups[0][0], which points to the first node of the selection internally. Fortunately, utilizing the selection.node() method will fetch this initial element accurately. Here is an example of how you can achieve this:

function mouseDate(scale){ 
  var g = d3.select("#group").node();
  var x0 = scale.invert(d3.mouse(g)[0]);
  console.log(x0);
}

I am having trouble reaching the _groups attribute in angular/d3js

Answer №1

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