2020-03-15 实现一个编译器

[fanmingfei]

let x=[1,2,3],sum=0;for(let i of x){sum+=i;}

写个编译器，编译成es5的语法，并运行成功

[wangshouren7]

function run(source) {
    const wrapper = {
        getStart(...params) {
            return '\r\n(function (' + `${params.toString()}` + ') {\r\n'
        },
        getEnd(...params) {
            return '\r\n})(' + `${params.toString()}` + ' )\r\n';
        }
    }

    source = source
        // let => var
        .replace(/\blet\b/g, 'var')
        //for循环加闭包
        .replace(/for\s?\(var\s[^{]+([^}]+\})+/g, _ => wrapper.getStart() + _ + wrapper.getEnd())
        //给for里的语句加闭包
        .replace(/(for\s?\(var\s(\w+)\s[^)]+\)\s?)([\s\S]+)/, (_, start, name, str) => {

            const left = [], right = [], bucket = str.split('');
            let index = 0;

            do {
                if (bucket[index] === '{') {
                    left.push('{')
                } else if (bucket[index] === '}') {
                    right.push('}');
                }
                index++;
            } while ((left.length !== right.length))

            const middle = `{${wrapper.getStart(name)}${str.slice(1, index - 1)}${wrapper.getEnd(name)}}`;
            const end = str.slice(index);

            return start + middle + end;
        })

    const output = wrapper.getStart() + source + wrapper.getEnd();
    eval(output);
    return output;
}