How to check if a file exist in nuxt

I'm on Nuxt 2.15.4 and i wanna check in my store codes if a file exist in nuxt directory by fs-extra package.

it is simple in modules because i can get files path by this code:

const path = require('path')
const fse = require('fs-extra');
const FilePath = path.join(this.options.rootDir, './static/myfile.json')
const fse = require('fs-extra');
fse.pathExists(FilePath, (err, exists) => {
    console.log(err) // => null
    console.log(exists) // => true
})

but in vuex store i dont have access to this.options.rootDir and this code is always return false:

export const actions = {
  async nuxtServerInit({dispatch, commit}) {
    if(process.server){
      const fse = require('fs-extra');
      fse.pathExists('~/static/myfile.json', (err, exists) => {
        console.log(err) // => null
        console.log(exists) // => false
      })
    }
  }
}

how can i get files fullpath or check if it exits??

#UPDATE

It looks like I had a little mistake in my file path so used ./static/myfile.json and the check is done!!

but got another problem!! I have another json file, when I'm trying to use Object.assign(mainfile, myfile) it won't work!!

here is a sample:

  async nuxtServerInit({dispatch, commit}) {
    let mainfile = require('../assets/mainfile.json')
    // if i use assign here it works and merge them together
    // let myfile = require('../assets/myfile.json')
    // Object.assign(mainfile, myfile)
    if(process.server){
      const fse = require('fs-extra');
      fse.pathExists('./static/myfile.json', (err, exists) => {
        if(exists){
          Object.assign(mainfile, myfile)
          commit('SET_FILE', mainfile); // this send the unmerged file to mutation
          console.log(mainfile); // but get the merged json here
        }
      })
      console.log(mainfile); // it is unmerged
    }
    console.log(mainfile); // it is unmerged
  }

Ok, thanks to @kissu I found out the problem. As kissu mentioned in his answer's comment, commit is synchronous; I tried await action but didn't get the result; so I used pathExistsSync instead and done!!

  async nuxtServerInit({dispatch, commit}) {
    let myfile = {}
    let mainfile = require('../assets/mainfile.json')
    if(process.server){
      const fse = require('fs-extra');
      if(fse.pathExistsSync('./static/myfile.json')){
          myfile = require('../assets/myfile.json')
          Object.assign(mainfile, myfile)
      }
    }
    await dispatch('setMyFile', mainfile)
  }

#Update

require('../assets/mainfile.json') still throw error if file doesn't exist even with if(fse.pathExistsSync('./static/myfile.json')) statement so:

  async nuxtServerInit({dispatch, commit}) {
    let myfile = {}
    let mainfile = require('../assets/mainfile.json')
    if(process.server){
      const fse = require('fs-extra');
      if(fse.pathExistsSync('./static/myfile.json')){
          myfile = readJsonSync('./static/myfile.json')
          Object.assign(mainfile, myfile)
      }
    }
    await dispatch('setMyFile', mainfile)
  }