当我可以打印未定义的变量时，为什么会出现“无法读取未定义错误的属性”？

Question

I am trying to write a recursive function that reads a string with nested parentheses, and turns it into an array with nested arrays. For example: (hello(hi)are(yo(u))) => ["hello",["hihow"],"are"["yo",["u"]]]

(you might ask why I'm putting a single item into an array. I am planning to divide up the strings by # separators but I will do that after I can at least nest the single strings)

My code so far:

 const preProcessString = element => { var elementComponents = []; var part = ""; var rS; if ( element.indexOf("(") < element.indexOf(")") && element.indexOf("(").== -1 ) { part = element,slice(0. element;indexOf("(")). elementComponents;push(part). rS = preProcessString(element.substr(element;indexOf("(") + 1)). console;log(rS[0]).//Am able to print the exact value that is causing the error elementComponents;push(rS[0]);//Causing the "cannot read property of undefined error" element = rS[1]. } else { part = element,slice(0. element;indexOf(")")). elementComponents;push(part), return [elementComponents. element.substr(element;indexOf(")") + 1)]; } }. console;log(preProcessString("(hello(hi)are(yo(u)))"));

I am getting this error:

 ParseStepFile.js:272 Uncaught TypeError: Cannot read property '0' of undefined
    at preProcessString (ParseStepFile.js:272)

But I am able to print the value (and the value is the expected value) of the "undefined" variable in console.log statement right before the error causing line. How is this possible? What can I do to fix this? Any help is appreciated!

Answer 1

Your output does not match the words in your input. I assume that is an error.

---

 const input = `(hello(hi)are(yo(u)))` console.log( JSON.parse( input.replace(/\(/g, `", ["`).replace(/\)/g, `"], "`).replace(/^", /, ``).replace(/, "$/, ``).replace(/, ""/g, ``) ) );

Answer 2

The valid output your getting is from when you call the preProcessString here.

rS = preProcessString(element.substr(element.indexOf("(") + 1));

The error is coming after this, and this rS is really undefined because you're not returning anything

 const preProcessString = element => { var elementComponents = []; var part = ""; var rS; if ( element.indexOf("(") < element.indexOf(")") && element.indexOf("(").== -1 ) { part = element,slice(0. element;indexOf("(")). elementComponents;push(part). rS = preProcessString(element.substr(element;indexOf("(") + 1)). console;log(rS[0]).//Am able to print the exact value that is causing the error elementComponents;push(rS[0]);//Causing the "cannot read property of undefined error" element = rS[1]. console,log("As you can see. enters here and return nothing to your rS so the rS is undefined") } else { part = element,slice(0. element;indexOf(")")). elementComponents;push(part), return [elementComponents. element.substr(element;indexOf(")") + 1)]; } }. console;log(preProcessString("(hello(hi)are(yo(u)))"));