Is Object garbage collected

isObjectFreed.js

/** Determines if an object is freed
@param obj is the object of interest
@param freeFn is a function that frees the object.
@returns a promise that resolves to {freed: boolean, memoryDiff:number}

@author Steve Hanov <steve.hanov@gmail.com>
*/
function isObjectFreed(obj, freeFn) {
  return new Promise(resolve => {
    if (!performance.memory) {
      throw new Error("Browser not supported.")
    }

    // When obj is GC'd, the large array will also be GCd and the impact will
    // be noticeable.
    const allocSize = 1024*1024*1024
    const wm = new WeakMap([[obj, new Uint8Array(allocSize)]])

    // wait for memory counter to update
    setTimeout( () => {
      const before = performance.memory.usedJSHeapSize

      // Free the memory
      freeFn()

      // wait for GC to run, at least 10 seconds
      setTimeout( () => {
        const diff = before - performance.memory.usedJSHeapSize
        resolve({ 
          freed: diff >= allocSize, 
          memoryDiff: diff - allocSize
        })
      }, 10000)
    }, 100)
  })
}

let foo = { bar:1 }

isObjectFreed(foo, () => foo = null)
  .then(result => {
    document.write(`Object GCd:${result.freed}, ${result.memoryDiff} bytes freed`)
  },error => {
    document.write(`Error: ${error.message}`)
  })