To remove an element with a specified key, use the .delete() method. It returns true if the element existed and has been removed, otherwise false.

const obj1 = {},
      obj2 = {};

const weakmap = new WeakMap([[obj1, 7]]);
console.log(weakmap.delete(obj1)); // true
console.log(weakmap.has(obj1)); // false
console.log(weakmap.delete(obj2)); // false