.json() is an async method (it returns a Promise itself), so you have to assign the parsed value in the next .then()
var obj;
fetch('https://jsonplaceholder.typicode.com/posts/1')
.then(res => res.json())
.then(data => {
obj = data;
})
.then(() => {
console.log(obj);
});Modern async/await equivalent
You have to await the .json() method.
async function foo() {
let obj;
const res = await fetch('https://jsonplaceholder.typicode.com/posts/1')
obj = await res.json();
console.log(obj)
}
foo();