Question

I created an external .js file with prototype:

function Logger() {
    var log = new Array("");
}

Logger.prototype.AddLine = function (value) {
    if (value) {
        Logger.log.push("\t" + value);
    }
}

Logger.prototype.ReadLog = function () {
    return this.log.join("");
}

And now I try to use it on my page. I included my file in the header. And I have simple js:

$(document).ready(function () {

        var log = new Logger();
        log.AddLine("User entered the page");
});

Firebug error:
TypeError: Logger.log is undefined
[Break On This Error]
Logger.log.push(“\t” + value);

Can anyone please explain why this is happening?

Answer 1

To set log on the Logger instance to an empty array, use this.log = [], not var log. The latter creates a private variable, which you can’t access outside the function.

Also, Logger.log means: access the log property on the Logger function. Here you want the instance instead, so use this.log (like you did in ReadLog).