javascript - codemod from ForInStatement to ForStatement -

i have codemod want transform

for (var key in foo){} 

into

for (var keys = 0; key < foo; key++){} 

i managed far:

return j(file.source)     .find(j.forinstatement)     .replacewith(p => {          var prop = p.node.left.declarations[0].id;          var v = [j.variabledeclarator(prop, null)];         var vardec = j.variabledeclaration('var', v);         var binary = j.binaryexpression('<', prop, j.identifier('foo'));         var ue = j.updateexpression('++', prop, false);         var block = j.blockstatement([]);          var forin = j.forstatement(vardec, binary, ue, block);         return forin;     })     .tosource(); 

and that brought me far:

for (var key; key < foo; key++)   {} 

i'm still bit lost creating things scratch...

question:

• am doing correct? feels quite verbose, maybe way go.
• how finish? missing example foo.length...

ps: felix, if reading this, point me can send pull requests improve docs! happy while trying learn api. oh, , felix, nice tool guys made!

creating ast nodes directly indeed verbose. however, jscodeshift exports helper "methods" allow generate ast nodes string , let interpolate existing ast nodes (tagged templates ftw!).

your above example simplified to:

  return j(file.source)     .find(j.forinstatement)     .replacewith(p => {       var prop = p.node.left.declarations[0].id;       return statement`for (var ${prop} = 0; ${prop} < foo.length; ${prop}++) ${p.node.body}`;     })     .tosource(); 

demo

note though template methods (expression, statement, statements) have limitations (you can interpolate ast nodes can put identifier).

---

if wanted create foo.length manually, have create memberexpression:

j.memberexpression(   prop,   j.identifier('length') );