isFunction (value) {
    return typeof value === 'function' || (value && toStr(value) === FUNC_TAG)
  }
Return whether the provided value is a function.

@example
import { utils } from 'js-data';
const a = function () { console.log('foo bar'); };
const b = { foo: "bar" };
console.log(utils.isFunction(a)); // true
console.log(utils.isFunction(b)); // false

@method utils.isFunction
@param {*} value The value to test.
@returns {boolean} Whether the provided value is a function.
@since 3.0.0