Copy a object properties to another in TypeScript, cause error TS2339

Question

I use a extend() function to extend a object:

function extend(obj: Object, extension: Object) {
    for (var key in obj) {
        try {
            extension[key] = obj[key];
        } catch (e) {
            console.error(e);
        }
    }
}

And there is a class Observer() hava a method Update() and a object check which is HTMLInputElement type.

class Observer {
    Update(value) { }
}
var check:HTMLInputElement = document.createElement("input");

I use extend() function to extend checkbox,so it would have the method Update().

extend(new Observer(), check);
check.Update = function(value) {
    this.checked = value;
}

And then cause error TS2339:Property 'Update' does not exist on type 'HTMLInputElement'

How to Fixed this error? Change the extend() function?

David Sherret · Accepted Answer · 2015-11-03 14:24:24Z

2

Might be a good scenario for an intersection type?

function extend<T, U>(obj: T, extension: U) {
    Object.keys(obj).forEach((key) => {
        extension[key] = obj[key];
    });

    return extension as T & U;
}

var check: HTMLInputElement;
var extended = extend(new Observer(), check);

// example HTMLInputElement property use
extended.attributes;
// no compile error here either:
extended.Update = function(value) {
    this.checked = value;
};

edited Nov 3, 2015 at 14:24

answered Nov 3, 2015 at 14:12

David Sherret

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Comments

MartyIX · Accepted Answer · 2015-11-03 14:17:11Z

0

Is the following code snippet, what you are looking for?

class Observer extends HTMLInputElement{
    Update: any;
}

var check:Observer = <Observer>document.createElement("input");

check.Update = function(value) {
    this.checked = value;
}

edited Nov 3, 2015 at 14:17

answered Nov 3, 2015 at 14:09

MartyIX

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