json.stringify可以将json对象转换为字符串

 <script>
        var obj = {
            name:"lisi",
            age:18
        }
        var arr = [
            {name:"lisi",age:14}
        ]
        // var res = JSON.stringify(obj);
        console.log(JSON.stringify(obj))
        console.log(JSON.stringify(arr))
        var str = `{"name":"李四","age":18}`
        var sum =JSON.parse(str)
        // json.parse可以将json格式的字符串转换为json对象
        console.log(sum)
    </script>

示例

 <script>
        var str = `
        [{"name":"李四666","data":[2019,10,11]},
        {"name":"张三666","data":[2019,10,11]},
        {"name":"王五点击666","data":[2019,10,11]}]
        `
        /*
        var arr = [
            {name:"李四...",data:"2019-10-11"}
        ]
        */
       var arr =JSON.parse(str)
       var list = [];
        arr.forEach(item=>{
            var {name,data}=item;
            name = name.replace(/\d/g,"")+"...";
            data = data.join("-")
            list.push({
                name,
                data
            })
        })
        console.log(list)
       //console.log(str.replace(reg,""))
    </script>

 <script>
        var arr =[
            {name:"lisi"},
            {name:"html"},
            {name:"css"},
            {name:"vue"},
            {name:"vue"},
            {name:"html"},
        ]
        // ["lisi","html","css","vue"]
        var list = []
        arr.forEach(item=>{
            var {name} = item;
           if(!list.includes(name)){
               list.push(name);
           }
        })
        console.log(list)
    </script>

 <script>
        var arr ={
            A:[{city:"武汉"},{city:"广州"}],
            B:[{city:"深圳"},{city:"广州"}],
            C:[{city:"上海"},{city:"武汉"}],
        }
        var list=[];
        for(var key in arr){
            console.log(arr[key])
            list.push(...arr[key]);
        }
        //console.log(list)
        var res =[];
        list.forEach(item=>{
            var {city} = item;
            console.log(item)
            if(!res.includes(city)){
                res.push(city);
            }
        })
        console.log(res)
    </script>