CODEWITHSUNDEEP
javascriptobject
Garth Smith
Garth Smith

Reputation: 103

Concatenating my object with a string

This question is for objects in Javascript.

I notice that I can add a string and an Error object just fine, and the Error object text is concatenated with no problems.

try {
    throw new Error('Sample Text');
} catch (error) {
    document.writeln('There was an error. ' + error); // Go plus sign!
}

This outputs There was an error. Error: Sample Text which is pretty cool. The Error object knew what string I wanted to concatenate. My own objects do not act nice like this.

var myObject = (function () {
    var text = 'Text I want to concat.',
        get_text = function () { return text; },
        that = {};
    that.get_text = get_text;
    return that;
}());
document.writeln('What does my object say: ' + myObject); // Uncool

My own object outputs What does my object say: [object Object] and does not act nice like the Error object does.

I do not want [object Object] to be output. How can I change what string myObject spits out when being added to a string?

Upvotes: 2

Views: 158

Answers (2)

Jameson
Jameson

Reputation: 6659

You need to provide a toString() method, as in the Java programming language.

(People are always making such a big deal out of how the languages are different, but really, they share some notable similarities, like this.)

For example, look at this bit of code:

function Apple() {
    this.toString = function() {
        return "I'm an Apple!" 
    }
}

var apple = new Apple();
document.write(apple);

For existing objects, you can add a toString method this way:

existingObject.prototype.toString = function() { 
    return "I am an existing objet.";
}

Upvotes: 1

Tikhon Jelvis
Tikhon Jelvis

Reputation: 68152

You should give your objects a toString method that returns the appropriate string. So you just need to rename get_text to toString. You could write it something like this:

var myObject = (function () {
    var text = 'Text I want to concat.';
    return {
      toString : function () { return text }
    };
}());

Upvotes: 3

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