javascript エラー「Uncaught SyntaxError: Invalid left-hand side in assignment」の解決方法

let x = 1;
let y = 2;

if (x = 1 || y = 3) {
  console.log('success');
}

Uncaught SyntaxError: Invalid left-hand side in assignment

Uncaught SyntaxError: invalid assignment left-hand side

let x = 1;
let y = 2;

if (x == 1 || y == 3) {
  console.log('success');
}

<p id="hoge">sample</p>

<script>

document.getElementById("foo") = function (){
    console.log("クリックされました")
}
// Uncaught ReferenceError: Invalid left-hand side in assignment

</script>

Uncaught ReferenceError: cannot assign to function call

<p id="hoge">sample</p>

<script>

document.getElementById("hoge").onclick = function (){
    console.log("クリックされました")
}

</script>

if (1 =< 2) {
  console.log('sample')
}

// Uncaught ReferenceError: Invalid left-hand side in assignment

Uncaught SyntaxError: invalid assignment left-hand side

if (1 <= 2) {
  console.log('sample')
}

let x = 1;
let y = 2;

if (x =< y) {
  console.log('success');
}

// Uncaught SyntaxError: Unexpected token '<'

Uncaught SyntaxError: expected expression, got '<'