javascript - Reactjs - Changing JSON based on state -


solved: solution on bottom

i have drop down menu changes current state of component. this:

<select onchange={event => this.setstate({typeoflist: event.target.value})}>   <option value="list.a">list a</option>   <option value="list.b">list b</option> </select>

the problem when set state throws me error click on item in menu. because have function changes json use list. here snippet of code:

json

const list = require("./list.json")

list.json huge, looks this:

{     "a":{         "objects":{             "term":["ball"],             "image":["./img/ball"]         }     },     "b":{         "objects":{             "term":["stick"],             "image":["./img/stick"]         }     }, }

state

constructor(props){ super(props)          this.state={             term:'',             typeoflist: list.a         }     }

function throws error

createarr(){     let item = this.state.typeoflist.split(/(\s)/)     let arr = []     for(var i=0;i<item.length;i++){         if(/(\[(.*?)\]|\((.*?)\))/g.test(item[i])){             arr.push(item[i])         }         (var key in this.state.typeoflist){             for(var j=0;j<this.state.typeoflist[key].term.length;j++){                 if (this.state.typeoflist[key].term[j] === item[i]){                     arr.push(item[i])                 }             }         }     }     return arr }

the console says "typeerror: cannot read property 'length' of undefined". function works until click list change state. i'm not sure if practice. how should changing list in json?

solution: called json object wrong way. did assign typeoflist string this:

constructor(props){   super(props)    this.state={     term:'',     typeoflist: "a"   } }

and called using [this.state.typeoflist] instead of typing this.state.typeoflist. can keys typing list[this.state.typeoflist][key]

"typeerror: cannot read property 'length' of undefined" because have set value of this.state.typeoflist[key] string. thus, this.state.typeoflist[key].term becomes undefined.

onchange={event => this.setstate({typeoflist: event.target.value})}

event.target.value string

i'm guessing need update value of term instead


Comments

Post a Comment

Popular posts from this blog

Is there a better way to structure post methods in Class Based Views -

i'm using class based views in django , never specify url in ajax calls , omit action parameter in form because know these requests go through post method of class based view. notice view - profile page make many requests depending on user updating on page - post method become convoluted , if/else mess example: def post(self, request, *args, **kwargs): # handle user changing available date if request.post.get('availabledate') != none: self.updateavailabledate(request) return jsonresponse({'result':'success'}) if request.post.get('newprojectname') != none: creative_user = creativeuserprofile.objects.get(id = request.user.id) project = project.create_project(creative_user, request.post['newprojectname']) project.save() return jsonresponse({'projectid': project.id }) if request.post.get('projectimage') != none , request.files['file']: proj
Read more

performance - Why is XCHG reg, reg a 3 micro-op instruction on modern Intel architectures? -

i'm doing micro-optimization on performance critical part of code , came across sequence of instructions (in at&t syntax): add %rax, %rbx mov %rdx, %rax mov %rbx, %rdx i thought had use case xchg allow me shave instruction , write: add %rbx, %rax xchg %rax, %rdx however, dimay found agner fog's instruction tables , xchg 3 micro-op instruction 2 cycle latency on sandy bridge, ivy bridge, broadwell, haswell , skylake. 3 whole micro-ops , 2 cycles of latency! 3 micro-ops throws off 4-1-1-1 cadence , 2 cycle latency makes worse original in best case since last 2 instructions in original might execute in parallel. now... cpu might breaking instruction micro-ops equivalent to: mov %rax, %tmp mov %rdx, %rax mov %tmp, %rdx where tmp anonymous internal register , suppose last 2 micro-ops run in parallel latency 2 cycles. given register renaming occurs on these micro-architectures, though, doesn't make sense me done way. why wouldn't register renamer
Read more

jquery - Responsive Navbar with Sub Navbar -

good day, forgive me nav vocabulary not best. if question confusing apologize. i'm working on navigation bar needs centered on page @ 768px , above. items in nav open (or perhaps toggle) subnav lives directly below. these nav should appear centered on page. i have been able work through responsive portion of nav bar, having main items align vertically , sub nav menu of each item roll out below, , gave them indent separation. working well. however, issue not responsive side, behavior @ width greater 768px. happens toggling menu's sub navigation pushes other main items down page below sub nav. here's code: $(document).ready(function () { //stick in fixed 100% height behind navbar don't wrap $('#slide-nav.navbar-inverse').after($('<div class="inverse" id="navbar-height-col"></div>')); $('#slide-nav.navbar-default').after($('<div id="navbar-height-col"></d
Read more