owl/doc/learning/how_to_debug.md

🦉 How to debug Owl applications 🦉

Non trivial applications become quickly more difficult to understand. It is then useful to have a solid understanding of what is going on. To help with that, logging useful information is extremely valuable. There is a javascript file which can be evaluated in an application.

Once it is executed, it will log a lot of information on each component main hooks. The following code is a minified version to make it easier to copy/paste:

function debugOwl(t,e){let n,o="[OWL_DEBUG]";function r(t){let e;try{e=JSON.stringify(t||{})}catch(t){e="<JSON error>"}return e.length>200&&(e=e.slice(0,200)+"..."),e}if(Object.defineProperty(t.Component,"current",{get:()=>n,set(s){n=s;const i=s.constructor.name;if(e.componentBlackList&&e.componentBlackList.test(i))return;if(e.componentWhiteList&&!e.componentWhiteList.test(i))return;let l;Object.defineProperty(n,"__owl__",{get:()=>l,set(n){!function(n,s,i){let l=`${s}<id=${i}>`,c=t=>console.log(`${o} ${l} ${t}`),u=t=>(!e.methodBlackList||!e.methodBlackList.includes(t))&&!(e.methodWhiteList&&!e.methodWhiteList.includes(t));u("constructor")&&c(`constructor, props=${r(n.props)}`);u("willStart")&&t.hooks.onWillStart(()=>{c("willStart")});u("mounted")&&t.hooks.onMounted(()=>{c("mounted")});u("willUpdateProps")&&t.hooks.onWillUpdateProps(t=>{c(`willUpdateProps, nextprops=${r(t)}`)});u("willPatch")&&t.hooks.onWillPatch(()=>{c("willPatch")});u("patched")&&t.hooks.onPatched(()=>{c("patched")});u("willUnmount")&&t.hooks.onWillUnmount(()=>{c("willUnmount")});const d=n.__render.bind(n);n.__render=function(...t){c("rendering template"),d(...t)};const h=n.render.bind(n);n.render=function(...t){const e=n.__owl__;let o="render";return e.isMounted||e.currentFiber||(o+=" (warning: component is not mounted, this render has no effect)"),c(o),h(...t)};const p=n.mount.bind(n);n.mount=function(...t){return c("mount"),p(...t)}}(s,i,(l=n).id)}})}}),e.logScheduler){let e=t.Component.scheduler.start,n=t.Component.scheduler.stop;t.Component.scheduler.start=function(){this.isRunning||console.log(`${o} scheduler: start running tasks queue`),e.call(this)},t.Component.scheduler.stop=function(){this.isRunning&&console.log(`${o} scheduler: stop running tasks queue`),n.call(this)}}if(e.logStore){let e=t.Store.prototype.dispatch;t.Store.prototype.dispatch=function(t,...n){return console.log(`${o} store: action '${t}' dispatched. Payload: '${r(n)}'`),e.call(this,t,...n)}}}
debugOwl(owl, {
  // componentBlackList: /App/,  // regexp
  // componentWhiteList: /SomeComponent/, // regexp
  // methodBlackList: ["mounted"], // list of method names
  // methodWhiteList: ["willStart"], // list of method names
  logScheduler: false,  // display/mute scheduler logs
  logStore: true,     // display/mute store logs
});

The above code, once pasted somewhere in the main javascript file of an owl application, will log information looking like this:

[OWL_DEBUG] TodoApp<id=1> constructor, props={}
[OWL_DEBUG] TodoApp<id=1> mount
[OWL_DEBUG] TodoApp<id=1> willStart
[OWL_DEBUG] TodoApp<id=1> rendering template
[OWL_DEBUG] TodoItem<id=2> constructor, props={"id":2,"completed":false,"title":"hey"}
[OWL_DEBUG] TodoItem<id=2> willStart
[OWL_DEBUG] TodoItem<id=3> constructor, props={"id":4,"completed":false,"title":"aaa"}
[OWL_DEBUG] TodoItem<id=3> willStart
[OWL_DEBUG] TodoItem<id=2> rendering template
[OWL_DEBUG] TodoItem<id=3> rendering template
[OWL_DEBUG] TodoItem<id=3> mounted
[OWL_DEBUG] TodoItem<id=2> mounted
[OWL_DEBUG] TodoApp<id=1> mounted

Each component has an internal id, which is very useful when debugging.

Note that it is certainly useful to run this code at some point in an application, just to get a feel of what each user action implies, for the framework.