JavaScript：从数组中排序整数和运算符

Question

Here is my jsfiddle: JSFIDDLE

So, I'm trying to get an output that shows 3 different objects:

// Wanting to get 
// {
// 0: {type: "number", value: 22},
// 1: {type: "operator", value: "+"},
// 2: {type: "number", value: 22},
// }

function lexer(contents) {
  const tokens = [];

  while (contents.length) {
    let char     = contents[0];
    contents = contents.slice(1);

    if (/[-+*\/]/.test(char)) {
      tokens.push({ type: 'operator', value: char });
    }

    let number = '';
    while (/[1-9]/.test(char)) {
      number += char;
      char = contents[0];
      contents = contents.slice(1);
    }

    if (number !== '') {
      tokens.push({ type: 'number', value: parseInt(number, 10) });
    }
  }
  return tokens;
}

const result = lexer(["2", "2", "+", "2", "2"]);

Now I'm just going to fill out more text. I'm not exactly sure what is wrong with this code as it seems to be skipping one of the outputs. I'm guessing it has something to do with the while loop.

Answer 1

Your issue is that you're slicing contents before verifying that it's a number. Thus, when it reaches the + it has already sliced it off of the array before it pushes the token and when the next loop with the condition contents.length comes around, the plus will have been dropped and you have no way to know that it was there.

I would suggest that instead of slicing right after reading the character, only slice once you've used the character in some way, ie after you've pushing the operator token or appended the char to number .

function lexer(contents) {
  const tokens = [];

  while (contents.length) {
    let char     = contents[0];

    if (/[-+*\/]/.test(char)) {
      tokens.push({ type: 'operator', value: char });
      contents = contents.slice(1);
    }

    let number = '';
    while (/[1-9]/.test(char)) {
      number += char;
      contents = contents.slice(1);
      char = contents[0];
    }

    if (number !== '') {
      tokens.push({ type: 'number', value: parseInt(number, 10) });
    }
  }
  return tokens;
}

It's a subtle difference, but this way you aren't changing your array until after you've used the data, thus ensuring consistency.

Updated fiddle: https://jsfiddle.net/semhw54y/10/