Utility for console logs preservation.

logPreservation.js

/**
 * Utility for console logs preservation.
 *
 * @example Enable logs preservation for next page load:
 * logPreservation.enable();
 *
 * @example Dump, but keep log entries for another dump:
 * logPreservation.dump(true);
 *
 * @author Maciej Nux Jaros
 * @license MIT
 */
function LogPreservation() {
	this.saved = [];

	this.failInitError = false;
	this.origConsole = {};

	this.restoreSettings();
	if (this.settings.enabled) {
		this.init();
	} else {
		this.failInitError = 'disabled';
	}
}
LogPreservation.prototype.init = function() {
	try {
		var me = this;
		this.capturedFunctions.forEach(function(level){
			me.origConsole[level] = console[level];
			console[level] = function() {
				me._save(level, arguments);
				me.origConsole[level].apply(console, arguments);
			};
		});
	} catch (e) {
		// save for debugging
		this.failInitError = e;
	}
};

// functions to replace and capture
LogPreservation.prototype.capturedFunctions = ['log', 'warn', 'error'];
// settings save key
LogPreservation.prototype.settingsKey = 'LogPreservation-settings-storage';
// settings
LogPreservation.prototype.settings = {
	enabled : false
};

/**
 * Enable for next time or temporarily pause saving logs.
 */
LogPreservation.prototype.enable = function() {
	this.settings.enabled = true;
	this.saveSettings();
};
/**
 * Disable for next time.
 */
LogPreservation.prototype.disable = function() {
	this.settings.enabled = false;
	this.saveSettings();
};
/**
 * Store settings ~permanently.
 */
LogPreservation.prototype.saveSettings = function() {
	localStorage.setItem(this.settingsKey, JSON.stringify(this.settings));
};
/**
 * Clear settings storage.
 */
LogPreservation.prototype.clearSettings = function() {
	localStorage.removeItem(this.settingsKey);
};
/**
 * Restore settings.
 *
 * @note missing keys will not be removed from current settings.
 */
LogPreservation.prototype.restoreSettings = function() {
	var settings = JSON.parse(localStorage.getItem(this.settingsKey));
	if (settings) {
		for (var i in settings) {
			this.settings[i] = settings[i];
		}
	}
};

/**
 * Save console data.
 *
 * @private
 *
 * @param {String} level
 * @param {Array} argumentsArray
 *		This is either arguments array or a real Array object
 *		(see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions_and_function_scope/arguments).
 * @returns {String}
 */
LogPreservation.prototype._save = function (level, argumentsArray) {
	if (!this.settings.enabled) {
		return;
	}
	this.saved.push({
		level : level,
		argumentsArray : argumentsArray,
		dt : (new Date()).toISOString()
	});
};

/**
 * Dump all saved messages to console.
 * @param {Boolean} preserve if true then messages are not cleared after dump.
 * @returns {undefined}
 */
LogPreservation.prototype.dump = function (preserve) {
	// disable pre-dump
	var enabledPrev = this.settings.enabled;
	this.settings.enabled = false;

	for (var i = 0; i < this.saved.length; i++) {
		var level = this.saved[i].level;
		var argumentsArray = this.saved[i].argumentsArray;

		// doesn't work on iOS (at least from weinre)
		//this.origConsole[level].apply(console, argumentsArray);
		console[level].apply(console, argumentsArray);
	}

	// reset state post-dump
	this.settings.enabled = enabledPrev;

	if (!preserve) {
		this.saved.length = 0;
	}
};

var logPreservation = new LogPreservation();