Learn about toString

Author: YunFeng Githubgithub.com/ihtml5

The problem

How do I get a function parameter? We all know that arguments can be used to get the value of a run-time argument, but how to get the value of a parameter

toString

Function. The prototype. There’s a phrase in the toString, said in a Function call the toString method directly, will return to the source code of this Function as a string. The important message here is how powerful and simple it is to decompile and parse the source of a function by calling toString().

/ / lu code
function tq(a, b, c) {}
tq.toString();
// "function tq(a, b, c) {}
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Several methods to get function parameters have been written by predecessors

1. Get-parameter-names is recommended

//https://github.com/goatslacker/get-parameter-names/blob/master/index.js
// If you can't read the re, go to https://regexper.com
var COMMENTS = /((\/\/.*$)|(\/\*[\s\S]*? \*\/))/mg;
var DEFAULT_PARAMS = /=[^,]+/mg;
var FAT_ARROWS = /=>.*$/mg;

function getParameterNames(fn) {
  var code = fn.toString()
    .replace(COMMENTS, ' ')
    .replace(FAT_ARROWS, ' ')
    .replace(DEFAULT_PARAMS, ' ');

  var result = code.slice(code.indexOf('(') + 1, code.indexOf(') '))
    .match(/([^\s,]+)/g);

  return result === null
    ? []
    : result;
}

module.exports = getParameterNames;
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2. It’s similar to 1

function getArgs(func) {
 // Get the string that matches the parameter pattern with the re.
 // The first grouping is this: ([^)]*) any character that is not a close parenthesis
 var args = func.toString().match(/function\s.*? \ \ (((^)] *)) /) [1];
 // Use commas to separate arguments (arguments string).
 return args.split(",").map(function(arg) {
  // Remove comments (inline comments) and Spaces
  return arg.replace(/ / \ \ *. *, *, / /."").trim();
 }).filter(function(arg) {
  // Make sure there is no undefined.
  return arg;
 });
}
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3. Zhihu shi Jun he offers a simpler approach

//https://www.zhihu.com/question/28912825/\(\s*([\s\S]*?) \s*\)/.exec(fn)[1].split(/\s*,\s*/)
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Method 1 takes into account single-line comments, multi-line comments, default values, arrow functions, and more adaptability. Method 1 is recommended

ToString Other uses

1. Object.prototype.toString

Determine the type of a variable. This is often used in libraries such as jquery

Object.prototype.toString.call(obj);
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2. Number.prototype.toString

Converting numbers to strings, such as 1 to ‘1’

3. Boolean.prototype.toString

 var b = true;
console.log(b.toString()); // 'true'
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4. Array.prototype.toString

[].join(‘,’);

[].toString() / /"
[1.2].toString() / / '1, 2,'
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5. Symbol.prototype.toString

Behavior is similar to the Function. The prototype. Will the toString Symbol Function source code parsing