This add-on function logs step using nerdamer

withsteps.js

nerdamer.register({
    parent: 'Helper',
    name: 'withsteps',
    visible: false,
    build: function() {
        var core = this;
        var operationLog = [];
        //write a function which would perform the log
        var log = function(operator, symbol1, symbol2, result, is_first) {
            if(!is_first) operationLog.pop();
            operationLog.push([symbol1, operator, symbol2, result]);
        };

        var operations = [
            ['add', '+'],
            ['subtract', '-'],
            ['divide', '/'],
            ['multiply', '*'],
            ['pow', '^']
        ];

        //use the set function to modify each operator function. Notice the use of a function 
        //to do this. This ensures each has its own scope
        var set = function(o, s) {
            core.PARSER.extend(o, function(symbol1, symbol2, f) { 
                var s1 = symbol1.text(), s2 = symbol2.text();
                //keep track of whether this function is still in a recursive loop
                core.PARSER.is_first = true;
                var result = f.call(this, symbol1, symbol2);
                log(s, s1, s2, result.text(), core.PARSER.is_first);
                //recursive loop is done
                core.PARSER.is_first = false;
                return result;//we got what we need so return the result

            }, true);
        };

        for(var i=0; i<operations.length; i++) {
            set(operations[i][0], operations[i][1]);
        }

        return function(expr_string) {
            operationLog = []; //clear the log
            var eq = nerdamer(expr_string);
            return [eq, operationLog];
        };
    }
});