Javascript Checkbox.checked Select All Function doesn't work. [Problem Solved] [duplicate]

<script>
       let SelectAll = document.querySelector('input')
        let items = document.querySelectorAll('input:nth-child(n+2)')
        // let a1 = SelectAll.checked
        // console.log(a1)
        

        SelectAll.onclick = function () {
            let SelectAll_status = SelectAll.checked
            console.log(SelectAll_status)
            // console.log(items.length)
            if (a1 = true) { 
          for (var i = 0;i < items.length;i++) {
            items[i].setAttribute("checked", "true");
        
          } } else {
            for (var j = 0;j < items.length;j++) {
            items[j].setAttribute("checked", "false");
            let return1 = items[j].checked
            
          }
          console.log (return1)
        }}
</script>

I use the If condition. But when I deselect the tick. Nothing works. Even the whole part of "Else" doesn't work.

At beginning, I used "items[i].checked= SelectAll.checked " , at console.log , "false" is given to items, but the tick toggle doesn't show. So,I need to use setAttribute. Then I need to use If conditions. And problems appear...

Updated Problem Solved ： if (SelectAll_status === true) ,here must be "===" ,not "=" .

for Else , setAttribute is not working. I change it to removeAttribute .It works.

let SelectAll = document.querySelector('input')
        let items = document.querySelectorAll('input:nth-child(n+2)')
       
        SelectAll.onclick = function () {
            let SelectAll_status = SelectAll.checked
            console.log(SelectAll_status)
            if (SelectAll_status === true) { 
          for (var i = 0;i < items.length;i++) {
            items[i].setAttribute("checked", "true");
        
          } } else {
            
            for (var j = 0;j < items.length;j++) {
             
            items[j].removeAttribute("checked");
            
            
          }
          
        }}

  form {
        border: 1px pink solid;
        width: 200px;
        background-image: linear-gradient(
          rgb(255, 226, 255),
          rgb(255, 250, 192)
        );
        color: rgb(121, 121, 121);
        margin: 20px auto;
      }
      hr {
        border: pink 1px solid;
      }

<form action="">
      <input type="checkbox" id="all" name="form1" />
      <label for="opt">Select ALL</label>
      <br />
      <hr />
      <input type="checkbox" id="opt1" name="form1" />
      <label for="opt1">111111</label>
      <br />
      <input type="checkbox" id="opt2" name="form1" ckecked />
      <label for="opt2">222222</label>
      <br />
      <input type="checkbox" id="opt3" name="form1" />
      <label for="opt3">333333</label>
      <br />
      <input type="checkbox" id="opt4" name="form1" />
      <label for="opt4">4444</label>
    </form>