move logic out to parent component.

equations/src/App.js

@@ -3,25 +3,46 @@ import {useEffect,useState} from 'react';
 import './App.css';
 
 function Equation(p) {
-	const {data} = p
-	const [operator,setOperator] = useState("disabled")
-	const [field,setField] = useState(Object.keys(data)[0])
+	const {data,id,equationParts,setEquationParts,field,operator} = p
 	
-	return <div style={{display:"inline-block",border:"1px solid black"}}>
-	<select onChange={(ev)=>{setField(ev.currentTarget.value)}}>
-	{Object.keys(data).map((key)=><option value={key}>{key}</option>)}
+	function updateEquation(field,operator) {
+		var eq = [...equationParts]
+		eq[id].field=field
+		eq[id].operator=operator
+		setEquationParts(eq)
+	}
+	return <><div style={{display:"inline-block",border:"1px solid black"}}>
+	<select onChange={(ev)=>{
+		updateEquation(ev.currentTarget.value,operator)
+	}}>
+	{Object.keys(data).map((key)=><option key={key} value={key}>{key}</option>)}
 	</select><br/>
-	{data[field]}</div>
+	{data[field]}</div><div style={{display:"inline-block",border:"1px solid black"}}>
+	<select onChange={(ev)=>{updateEquation(field,ev.currentTarget.value)}}>
+	{["+","-","x","÷","()"].map((key)=><option key={key} value={key}>{key}</option>)}
+	</select><br/>{id}</div></>
 }
 
 function EquationBuilder(p) {
 	const {data} = p
-	const [equationParts,setEquationParts] = useState([<Equation data={data}/>])
+	const [equationParts,setEquationParts] = useState([])
+	const [equation,setEquation] = useState([])
+	useEffect(()=>{
+		var newEq = []
+		for (var i=0;i<equationParts.length;i++) {
+			newEq.push(data[equationParts[i].field])
+			newEq.push(equationParts[i].operator)
+		}
+		setEquation(newEq)
+	},[equationParts])
 	return <>
 		<button onClick={()=>{
-			setEquationParts([...equationParts,<Equation data={data}/>])}}>+</button>
+			setEquationParts([...equationParts,{field:Object.keys(data)[0],operator:"+"}])}}>+</button>
+		<br/><br/>
+		{equationParts.map((eq,i)=><Equation equationParts={equationParts} setEquationParts={setEquationParts} id={i} data={data} field={equationParts[i].field} operator={equationParts[i].operator}/>)}
 		<br/><br/>
-		{equationParts.map((eq)=>eq)}</>
+		{equation}
+		</>
 }
 
 function App() {