ga and pendo install script explain

ga.js

(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
    (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
    m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
    })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
    
ga('create', 'UA-XXXXX-Y', 'auto');
ga('send', 'pageview');


function installGA() {
    window['GoogleAnalyticsObject'] = 'ga';
    window['ga'] = window['ga'] || function () {
        window['ga'].q = window['ga'].q || [];
        window['ga'].q.push(arguments);
    };
    window['ga'].l = 1 * new Date();

    a = document.createElement('script');
    a.async = 1;
    a.src = 'https://www.google-analytics.com/analytics.js'
    m = document.getElementsByTagName('script')[0];
    m.parentNode.insertBefore(a, m);

    ga('create', 'UA-XXXXX-Y', 'auto');
    ga('send', 'pageview');
};

pendo.js

(function (apiKey) {
    (function(p,e,n,d,o){var v,w,x,y,z;o=p[d]=p[d]||{};o._q=[];
    v=['initialize','identify','updateOptions','pageLoad'];for(w=0,x=v.length;w<x;++w)(function(m){
    o[m]=o[m]||function(){o._q[m===v[0]?'unshift':'push']([m].concat([].slice.call(arguments,0)));};})(v[w]);
    y=e.createElement(n);y.async=!0;y.src='https://cdn.pendo.io/agent/static/'+apiKey+'/pendo.js';
    z=e.getElementsByTagName(n)[0];z.parentNode.insertBefore(y,z);})(window,document,'script','pendo');
})('<ACTUAL_API_KEY_HERE>');



function installPendo() {
    window['pendo'] = window['pendo'] || {};
    o = window['pendo'];
    o._q = [];
    ['initialize','identify','updateOptions','pageLoad'].forEach(methodName => {
        window['pendo'][methodName] = window['pendo'][methodName] || function () {
            if (methodName === 'initialize') {
                o._q.unshift(['initialize'].concat([].slice.call(arguments, 0)));
            } else {
                o._q.push([methodName].concat([].slice.call(arguments, 0)));
            }
        };
    })

    y = document.createElement('script');
    y.async = 1;
    y.src = 'https://cdn.pendo.io/agent/static/YOURAPIKEY/pendo.js';
    z = document.getElementsByTagName('script');
    z.parentNode.insertBefore(y, z);

    pendo.initialize({
        visitor: {
            id: 1,
            other_prop: 2,
            another_prop: 3
        },
        account: {

        }
    })
}

this.js

//in global(window)

function f() {console.log(arguments);console.log(this);}
f(1,2,3)
// -> Arguments(3) [1, 2, 3, callee: ƒ, Symbol(Symbol.iterator): ƒ] 
// -> Window {window: Window, self: Window, document: document, name: "", location: Location, …}

// Why `this` points to Window ? Because f(1,2,3) is `window.f(1,2,3)`, `window` will be the `this` in `f`, 
// e.g. `abc.func()`, `abc` will be the `this` in `func`

// NEW
// function Product(category){this.category = category;}
// Product('tech') -> window.category is 'tech'
// p = new Product('tech') -> p.category is 'tech'

// CALL / APPLY
// Array.prototype.slice.call(arguments) Or [].slice.call(arguments)
// [1,2,3].slice -> [1,2,3] will be the `this` in `slice`
// But call / apply are different, they can change `this` for the method
// e.g. [].slice.call(arguments) -> call `slice` method on Array, and change the `this` in slice with `arguments`

function f2() {console.log([].slice.call(arguments));}
f2(1,2,3)
// -> [1,2,3] <- this is an array!