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