[Javascript AST] 2. Write a simple ESLint rule

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What we want to do is checking if user write nested if statements which actually can combine to one:

// BADif (a) {  console.log("a");} else {   if (b) {    console.log("b");  } }// GOODif (a) {  console.log("a");} else if (b) {    console.log("b");  } }////////////////////////// BADif (a) {   if (b) {    console.log("b");   } } // GOODif (a) {  console.log("a");   if (b) {    console.log("b");   } } // GOODif (a && b) {    console.log("b");} 

 

Notice that if statement can write with block statement or without block statem, such as:

if(a)  if(b)    console.log(‘b‘)

 

Rule:

export default function(context) {  return {    IfStatement(node) {      var ancestors = context.getAncestors(),        parent = ancestors.pop(),        grandparent = ancestors.pop();      if (typeof grandparent === "undefined") {        return;      }      if (        (parent.type === "BlockStatement" && // if has if() { if() {}}, nested if‘s parent is a BlockStatement        parent.body.length === 1 && // if() { console.log(); if() {} }, we consider this is fine          grandparent.type === "IfStatement") || // grandparent should be a if statement        parent.consequent === node // sometime we write if() something, don‘t have blockstatement, then we check consequent should be the node iteself      ) {        context.report(node, "nested if statement");      }    }  };}

 

 

 

[Javascript AST] 2. Write a simple ESLint rule