Why doesn't if statement check the status of the HTTP request below?

Question

After sending an HTTP request I check if the status is 200, then resolve(), but the if statement doesn't seem to work.

function getMelumat() {
  let promise = new Promise((resolve,reject)=>{
        let xhr = new XMLHttpRequest();
        xhr.open("GET",'https://jsonplaceholder.typicode.com/posts');
        xhr.send()
        xhr.onload = ()=>{
            if ( this.status == 200){
                resolve(this.response)
            }
            else {
               throw "AN ERROR OCCURED"
            }
          }
        })

     return promise

    }
         getMelumat().then(data=>{
                return JSON.parse(data)
            }).then(data=>{
                console.log(data)
            })

Answer 1

Checking if the status is 200 is not enough; you also need to check this.readyState.

The headers (with the status) will already be available at this.readyState == 2, but the whole response won't be complete until this.readyState == 4.