cannot read property in javascript code example

Example 1: cannot read property

/* This error occurs in Chrome Browser when you read a property or call 
a method on an undefined object. */
// To handle it, use "Optional Chaining" compatible with Node.js v14.0.0

Syntax -> ?.
Usage ->
let obj;
console.log(obj.a) // Cannot read property 'a' of undefined
console.log(obj?.a) // Works like a charm

Example 2: cannot read property

Seems like one of your values, with a property key of 'value' is undefined. Test that i1, i2and __i are defined before executing the if statements:

var i1 = document.getElementById('i1');
var i2 = document.getElementById('i2');
var __i = {'user' : document.getElementsByName("username")[0], 'pass' : document.getElementsByName("password")[0] };
if(i1 && i2 && __i.user && __i.pass)
{
    if(  __i.user.value.length >= 1 ) { i1.value = ''; } else { i1.value = 'Acc'; }

    if(  __i.pass.value.length >= 1 ) { i2.value = ''; } else { i2.value = 'Pwd'; }
}