func.js

function loadSomething(a, b, nextPage = 1) {
  console.log({ a, b, nextPage })
}

function loadInventorySearch({ a, b, nextPage = 1 }) {
  console.log({ a, b, nextPage })
}

// Do not pass nextPage
loadSomething(10, 20) // a: 10, b: 20, nextPage: 1

// Pass int as nextPage
loadSomething(10, 20, 30) // a: 10, b: 20, nextPage: 30

// Pass undefined as nextPage
loadSomething(10, 20, undefined) // a: 10, b: 20, nextPage: 1

// Pass null as nextPage
loadSomething(10, 20, null) // a: 10, b: 20, nextPage: null !!!!!!!

class SomeReactClass {
  loadInventorySearch = (nextPage) => {
    const { a, b } = this.props 
    const props = { b, a }

    if (nextPage) {
      props.page = nextPage
    }

    return loadInventorySearch(props)
  }

  loadSomething = (nextPage) => {
    const { a, b } = this.props

    if (nextPage) {
      return loadSomething(a, b, nextPage)
    }

    return loadSomething(a, b)
  }
}