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Chrome console & Debugging

Chrome console .. & debuging in chrome ..

• logging with console.log(...)
• breakpoints & debugger cmd, execution tracking …

‘use strict’

To enable ES5

• off by default — always put 'use script' on top of script/fn-body
  • auto enable for class & module
  • no way to cancel once enter strict mode
• non-strict: assignment to non-existing var (without declear) ==> create a new global var (for compatibility) ..

async actions: init now but finish later (code below it won’t wait) ..

Callback

loadScript('xxx.js', (error, script) => { .. }) (“error-1st” cb style) ..: cb hell / pyramid of doom
Fn Call Scheduling: setTimeout/setInterval(..) .. (enqueue in macrotask ..)

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let timerId = setTimeout/setInterval(fn, delay=0, ...args); // keep fn-ref in scheduler (not GC) 
clearTimeout/clearInterval(timerId); // "timerId keep same" af clear (not null)

• setTimeout(): set this=window ..
• setInterval(): fn-exe-time > delay? …
• nested setTimeout vs setInterval ..
• tasks: Output every second

JS intro

• init to make webpages alive .., run on platforms with JS engine (in browser aka “JS VM”, e.g. “V8” in Chrome & Opera) ..
  • browser env: window (root obj) => JS / DOM / BOM ..
  • BOM: navigator obj, location.href, model win fn: alert(), prompt(), confirm() ..
• JS in HTML: <script>..</script> & <script src=..></script> ..
  • type="text/javascript" language="javascript" attr no need anymore ..
  • inline content ignored if src set ..
  • browser cache external script for re-use ..
• in-browser JS restrictions …

Var, Data types & Ops

Var

• let, const: block scope .. — the old “var” & IIFE

Data types

• dynamic typed, 7+1 basic data types
• typeof — null: “object”, alert: “function” ..