Watch me do (step by step) a basic manual minification of basic JavaScript file

minified.js

//212 bytes
function codepoints(ΔstringΔ) {
  return ΔstringΔ.replace(/./g, function(ΔstringΔ) {
    return ΔstringΔ.charCodeAt(0) + " ";
  }).trim().replace(/ /g, ",");
}
alert(codepoints("JavaScript Packer"));

//first lets get rid of uneeded whitespace and linebreaks

//170 bytes
function codepoints(ΔstringΔ){return ΔstringΔ.replace(/./g,function(ΔstringΔ){return ΔstringΔ.charCodeAt(0)+" "}).trim().replace(/ /g,",")}alert(codepoints("JavaScript Packer"));

//lets shorten the variable name string passed inside function

//150 bytes
function codepoints(r){return r.replace(/./g,function(r){return r.charCodeAt(0)+" "}).trim().replace(/ /g,",")}alert(codepoints("JavaScript Packer"));

//we see replace command is used twice, lets make it once showed

//150 bytes (no gain this time)
function codepoints(r){return r[$='replace'](/./g,function(r){return r.charCodeAt(0)+" "}).trim()[$](/ /g,",")}alert(codepoints("JavaScript Packer"));

//we really do not need a function name for basic demo

//128 bytes
alert(function(a){return a[$="replace"](/./g,function(a){return a.charCodeAt(0)+" "}).trim()[$](/ /g,",")}("JavaScript Packer"))