How can we assign various class names depending on the value of an object?

Question

How can we assign various class names depending on the value of an object?

I have a set of objects stored in my component. I need to dynamically apply different classes based on the value of the ErrorLevel property within each object. If an object has ErrorLevel equal to 1, I want to assign the following classes to various elements:

class-red
class-container-red
class-message-red

If the ErrorLevel is not equal to 1, I would like to assign the following classes to the elements instead:

class-yellow
class-container-yellow
class-message-yellow

Is there a more efficient way to achieve this using Angular or CSS (or SASS) without having separate methods for each individual class?

Here is an example code snippet showcasing what I currently have:

<html>
<body>
<div *ngFor="let obj of myObjects">
<h1 [ngClass]="getCssClass(obj.ErrorLevel)"></h1>
<p [ngClass]="getCssClass2(obj.ErrorLevel)"></p>
<div [ngClass]="getCssClass3(obj.ErrorLevel)"></div>
</div>
</body>
</html>

export interface MyObject {
    Id: number;
    ErrorLevel: number;
}

@Component({
  selector: 'my',
  templateUrl: './my.component.html',
  styleUrls: ['./my.component.scss']
})
export class MyComponent implements OnInit {
  @Input() myObjects: MyObject[];

  constructor() { }

  ngOnInit() {
  }

  getCssClass(errrorLevel) {
    if(errrorLevel === 1) {
      return "class-red";
    } else {
      return "class-yellow";
    }
  }

  getCssClass2(errorLevel) {
    if(errrorLevel === 1) {
      return "class-container-red";
    } else {
      return "class-container-yellow";
    }
  }

  getCssClass3(errorLevel) {
    if(errrorLevel === 1) {
      return "class-message-red";
    } else {
      return "class-message-yellow";
    }
  }
}

css angular sass

Answer 1

Answer №1

Here is a suggestion for styling your HTML elements using Angular syntax:

<div [class.class-red]="errorLevel === 1" [class.class-yellow]="errorLevel !== 1"></div>

This code will add the specified class based on the condition being true.

Alternatively, you can follow xyz's solution, but I personally prefer using the [ngClass] syntax as it tends to be more readable.

I want to point out that naming your CSS classes starting with "class-" is unnecessary since the period in CSS already indicates it is a class. Just use names like red instead of class-red.

For a more efficient approach, consider placing the class on the parent div rather than individual elements:

<div [class.red]="object.ErrorLevel === 1" [class.yellow]="object.ErrorLevel !== 1" *ngFor="let object of myObjects">
    <h1>...</h1>
    <p>...</p>
    <div>...</div>
</div>

Then use CSS to style the child elements based on the parent class:

.red h1 {
    // styles for red h1
}
.red p {
    // styles for red p
}
...
.yellow div {
    // styles for yellow div
}

This method is recommended for several reasons:

Easier maintenance with one class applied to a single element, reducing the need to update multiple places when adding new color options.
Improved readability by centralizing the styling logic in one location.
Better performance as Angular only monitors changes on one element rather than multiple ones.

Answer 2

Here is a suggestion for styling your HTML elements using Angular syntax:

<div [class.class-red]="errorLevel === 1" [class.class-yellow]="errorLevel !== 1"></div>

This code will add the specified class based on the condition being true.

Alternatively, you can follow xyz's solution, but I personally prefer using the [ngClass] syntax as it tends to be more readable.

I want to point out that naming your CSS classes starting with "class-" is unnecessary since the period in CSS already indicates it is a class. Just use names like red instead of class-red.

For a more efficient approach, consider placing the class on the parent div rather than individual elements:

<div [class.red]="object.ErrorLevel === 1" [class.yellow]="object.ErrorLevel !== 1" *ngFor="let object of myObjects">
    <h1>...</h1>
    <p>...</p>
    <div>...</div>
</div>

Then use CSS to style the child elements based on the parent class:

.red h1 {
    // styles for red h1
}
.red p {
    // styles for red p
}
...
.yellow div {
    // styles for yellow div
}

This method is recommended for several reasons:

Easier maintenance with one class applied to a single element, reducing the need to update multiple places when adding new color options.
Improved readability by centralizing the styling logic in one location.
Better performance as Angular only monitors changes on one element rather than multiple ones.

Answer 3

Answer №2

If your project requires managing more than 2-3 error color cases, I suggest the following approach:

interface IError {
   id: string;
   color: string;
}

var errors: { [id: string]: IError; } = {
   "e1": { id: "1", color: "class-red" },
   "e2": { id: "3", color: "class-yellow" },
   ...
   "en": { id: "n", color: "class-n" }
};

Then, you can proceed to implement the getValueById method.

UPDATE: You may consider implementing a similar solution like the one below. Please excuse any potential errors as this was written in notepad. :)

interface IErrors<T> {
    add(key: string, value: T): void;
    remove(key: string): void;
    containsKey(key: string): boolean;
    keys(): string[];
    values(): T[];
    errorClass(key: string): T;
}

class Dictionary<T> implements IErrors<T> {

    _keys: string[] = [];
    _values: T[] = [];

    constructor(init?: { key: string; value: T; }[]) {
        if (init) {
          for (var x = 0; x < init.length; x++) {
            this[init[x].key] = init[x].value;
            this._keys.push(init[x].key);
            this._values.push(init[x].value);
          }
        }
    }

    add(key: string, value: T) {
        this[key] = value;
        this._keys.push(key);
        this._values.push(value);
    }

    remove(key: string) {
        var index = this._keys.indexOf(key, 0);
        this._keys.splice(index, 1);
        this._values.splice(index, 1);

        delete this[key];
    }

    keys(): string[] {
        return this._keys;
    }

    values(): T[] {
        return this._values;
    }

    containsKey(key: string) {
        if (typeof this[key] === "undefined") {
          return false;
        }

        return true;
    }
    errorClass(key: string): T {
        return this[_keys]._values;
    }
}

Answer 4

If your project requires managing more than 2-3 error color cases, I suggest the following approach:

interface IError {
   id: string;
   color: string;
}

var errors: { [id: string]: IError; } = {
   "e1": { id: "1", color: "class-red" },
   "e2": { id: "3", color: "class-yellow" },
   ...
   "en": { id: "n", color: "class-n" }
};

Then, you can proceed to implement the getValueById method.

UPDATE: You may consider implementing a similar solution like the one below. Please excuse any potential errors as this was written in notepad. :)

interface IErrors<T> {
    add(key: string, value: T): void;
    remove(key: string): void;
    containsKey(key: string): boolean;
    keys(): string[];
    values(): T[];
    errorClass(key: string): T;
}

class Dictionary<T> implements IErrors<T> {

    _keys: string[] = [];
    _values: T[] = [];

    constructor(init?: { key: string; value: T; }[]) {
        if (init) {
          for (var x = 0; x < init.length; x++) {
            this[init[x].key] = init[x].value;
            this._keys.push(init[x].key);
            this._values.push(init[x].value);
          }
        }
    }

    add(key: string, value: T) {
        this[key] = value;
        this._keys.push(key);
        this._values.push(value);
    }

    remove(key: string) {
        var index = this._keys.indexOf(key, 0);
        this._keys.splice(index, 1);
        this._values.splice(index, 1);

        delete this[key];
    }

    keys(): string[] {
        return this._keys;
    }

    values(): T[] {
        return this._values;
    }

    containsKey(key: string) {
        if (typeof this[key] === "undefined") {
          return false;
        }

        return true;
    }
    errorClass(key: string): T {
        return this[_keys]._values;
    }
}

How can we assign various class names depending on the value of an object?

Answer №1

Answer №2

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