chaijs-断言库简单实现

最近研究一下Chai, 发现其示例代码挺有意思的，就自己实现一下，

官方示例：

var expect = chai.expect;expect(foo).to.be.a('string');expect(foo).to.equal('bar');expect(foo).to.have.lengthOf(3);expect(tea).to.have.property('flavors')  .with.lengthOf(3);

简单实现上面代码功能：

const expect = (source, errMsg = 'Error') => {    const equal = (target) => {        if (source !== target) {            throw new Error(errMsg)        } else {            return {                to: to            }        }    }    const be = {        a (target) {            if (typeof source !== target) {                throw new Error(errMsg)            } else {                return {                    to: to                }            }        }    }    const haveFactory =  (source) => {        return {            lengthOf (target) {                if (source.length !== target) {                    throw new Error(`${errMsg}： actual: ${source.length}, expect: ${target}`)                } else {                    return {                        with: this,                        to: to                    }                }            },            property (target) {                if (!source.hasOwnProperty(target)) {                    throw new Error(errMsg)                } else {                    return {                        with: haveFactory(source[target]),                        to: to                    }                }            }        }                }    const to = {        equal,        be,        have: haveFactory(source, errMsg)    }    return { to }}const foo  = 'bar'const tea = {    flavors: 'abcd'}try {    expect(foo).to.be.a('string');    expect(foo).to.equal('bar');    expect(foo).to.have.lengthOf(3);    expect(tea).to.have.property('flavors').with.lengthOf(3);    } catch (error) {    console.log(error.message)}// output// Error： actual: 4, expect: 3