Creating Objects from Class Names in JavaScript ES6
When attempting to create an object factory in ES6 using the traditional old-style syntax, you may encounter an error. This is because the old syntax is incompatible with the new ES6 syntax.
In the provided code snippet:
export class Column {}
export class Sequence {}
export class Checkbox {}
export class ColumnFactory {
constructor() {
this.specColumn = {
__default: 'Column',
__sequence: 'Sequence',
__checkbox: 'Checkbox'
};
}
create(name) {
let className = this.specColumn[name] ? this.specColumn[name] : this.specColumn['__default'];
return new window[className](name); // this line throw error
}
}
let factory = new ColumnFactory();
let column = factory.create('userName');
The error occurs in the line return new window[className](name); because it attempts to access the class name as a global variable. This approach fails in ES6, as classes are not exposed as global variables.
Solution:
To resolve this issue, replace the class names in the specColumn object with the actual class references:
export class Column {}
export class Sequence {}
export class Checkbox {}
export const columnFactory = {
specColumn: {
__default: Column, // <--
__sequence: Sequence, // <--
__checkbox: Checkbox // <--
},
create(name, ...args) {
let cls = this.specColumn[name] || this.specColumn.__default;
return new cls(...args);
}
};
By doing so, you no longer rely on class names being available globally and can access classes directly from the specColumn object.
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