Some attempts at python style list comprehension in js

listComp.js

// ##########################################################
// pythonic list comprehension in js
// (as a toy task to test out github.com/metakirby5/codi.vim)
// ##########################################################

// ####################################
// first method: ~rust style. heavy WIP
// ####################################
String.prototype.for = function(inp) {
    return inp.map(eval("x => " + this))
}
Array.prototype.if = function(inp) {
    return this.filter(eval("x =>" + inp))
}

// ###### driver code ######
let arr = [1, 2, 3, 4, 5, 6, 7]
let out = 'x+1'.for(arr).if('x > 5')

// #############################
// second method: true pythonic!
// #############################
function c(str) {
    let condIdx = str.indexOf('if')
    let stoppingIdx = condIdx

    let cond = str.slice(condIdx+2)
    let arr = str.slice(str.indexOf("in") +2, stoppingIdx)
    let mod = str.slice(0, str.indexOf("for"))
    let mid = str.slice(str.indexOf("for")+3, str.indexOf("in")).trim()

    if (condIdx == -1) {
	    stoppingId = str.length
	    cond = true
	    arr = str.slice(str.indexOf("in") +2)
    }

    let out = []

    const modFunc = eval(mid + " => " + mod)
    let toParse = `${arr}.forEach(${mid} => { if (${cond}) out.push(modFunc(${mid.replace(/[()]/g, '')})) })`
    eval(toParse)
    return out
}

// ###### driver code ######
let a = [0, 1, 2, 3, 4, 5, 6]
let res = c('y+12 for y in a if y < 4')
// > [ 12, 13, 14, 15 ]

let b = [true, false, false, true]
let rrres = c('[i, v] for (v,i) in b')
// > [ [ 0, true ], [ 1, false ], [ 2, false ], [ 3, true ] ]

let strings = ["dog", "orange", "bar"]
let tought = c('x for (x,y) in strings if y > 1')
// > [ 'bar' ]

let s = c(`[ ${c(`[${c('p for p in [1, 2, 3]')}] for l in [1, 2]`)} ] for x in [1, 2, 3]`)
// > [ [ 1, 2, 3, 1, 2, 3 ], [ 1, 2, 3, 1, 2, 3 ], [ 1, 2, 3, 1, 2, 3 ] ]