lodash after

code

// createMathOperation.js
import baseToNumber from './baseToNumber.js'
import baseToString from './baseToString.js'

/**
 * Creates a function that performs a mathematical operation on two values.
 *
 * @private
 * @param {Function} operator The function to perform the operation.
 * @param {number} [defaultValue] The value used for `undefined` arguments.
 * @returns {Function} Returns the new mathematical operation function.
 */
function createMathOperation(operator, defaultValue) {
  return (value, other) => {
    if (value === undefined && other === undefined) {
      return defaultValue
    }
    if (value !== undefined && other === undefined) {
      return value
    }
    if (other !== undefined && value === undefined) {
      return other
    }
    if (typeof value === 'string' || typeof other === 'string') {
      value = baseToString(value)
      other = baseToString(other)
    }
    else {
      value = baseToNumber(value)
      other = baseToNumber(other)
    }
    return operator(value, other)
  }
}

export default createMathOperation

import createMathOperation from './.internal/createMathOperation.js'

/**
 * Adds two numbers.
 *
 * @since 3.4.0
 * @category Math
 * @param {number} augend The first number in an addition.
 * @param {number} addend The second number in an addition.
 * @returns {number} Returns the total.
 * @example
 *
 * add(6, 4)
 * // => 10
 */
const add = createMathOperation((augend, addend) => augend + addend, 0)

export default add

example

console.log(_.add('111', '111')); // "111111"
console.log(_.add('111', undefined)); // "111"
console.log(_.add('111', null)); // "111null"
console.log(_.add(111, null)); // 111
console.log(_.add(6, 6)); // 12

参数是number对输入非number数据做了一些防御处理；