Nightwatch custom assertion for No Console Errors

noConsoleErrors.js

/**
 * Checks that the browser console log currently contains zero errors
 * 
 * ```
 *    this.demoTest = function (client) {
 *      browser.assert.noConsoleErrors("Checking console for errors");
 *    };
 * 
 *    this.demoTest = function (client) {
 *      browser.assert.noConsoleErrors("reports/console.log","Checking console for errors");
 *    };
 * ```
 *
 * @method noConsoleErrors
 * @param {string} logfile Optional logfile to write the console log to 
 * @param {string} msg Optional log message to display in the output. If missing, one is displayed by default.
 * @api assertions
 * 
 */

var util = require('util');

exports.assertion = function(logfile,msg) {

    this.timeout=0
    
    this.formatMessage = function() {
        const message = msg || 'Checking console for errors. ';

        return {
            message,
            args: []
        }
    };
    
    this.expected = '0 console errors';

    this.actual = function(passed){
        return passed ? 'No console errors' : 'Found console errors'
    }
    
    this.evaluate = function(value){
        if(value == 0) return true;
        return false;
    }

    this.value = function(result){
        var errors = [];
        if(result && (result instanceof Array)){
            errors = result.filter(function(log) {
                return ((log.level == "SEVERE") && (!log.message.includes('favicon')));
            });
        }

        return errors.length;
    }

    this.command = function(callback){
        return this.api.getLog('browser', callback);
    }
}