Question

In the chrome developer console, type $x.toString() ($x is one of the built-in functions of the dev tools console). The output looks like this:

"bound: function (xpath, context)
    {
        var doc = (context && context.ownerDocument) || inspectedWindow.document;
        var result = doc.evaluate(xpath, context || doc, null, XPathResult.ANY_TYPE, null);
        switch (result.resultType) {
        case XPathResult.NUMBER_TYPE:
            return result.numberValue;
        case XPathResult.STRING_TYPE:
            return result.stringValue;
        case XPathResult.BOOLEAN_TYPE:
            return result.booleanValue;
        default:
            var nodes = [];
            var node;
            while (node = result.iterateNext())
                nodes.push(node);
            return nodes;
        }
    }"

What is the meaning of “bound: “, in the first line?

Answer 1

$x is a builtin function in webkit Developer Tools’ console, like $, $$ and others. The CommandLineAPI (used for console script evaluation) overwrites all the console methods’ toString functions to include the "bound: " prefix:

function bind(thisObject, memberFunction)
{
    var func = memberFunction;
    var args = Array.prototype.slice.call(arguments, 2);
    function bound()
    {
        return func.apply(thisObject, args.concat(Array.prototype.slice.call(arguments, 0)));
    }
    bound.toString = function() {
        return "bound: " + func;
    };
    return bound;
}

A full list of console functions wrapped this way can be found here.