JSFiddle - React, Tailwind, and code Playground

JavaScript

var data = [{"Body Weight":114," Untrained": 80," Novice": 145," Intermediate": 175," Advanced": 240," Elite": 320},
{"Body Weight":123," Untrained": 85," Novice": 155," Intermediate": 190," Advanced": 260," Elite": 345},
{"Body Weight":132," Untrained": 90," Novice": 170," Intermediate": 205," Advanced": 280," Elite": 370},
{"Body Weight":148," Untrained": 100," Novice": 190," Intermediate": 230," Advanced": 315," Elite": 410},
{"Body Weight":165," Untrained": 110," Novice": 205," Intermediate": 250," Advanced": 340," Elite": 445},
{"Body Weight":181," Untrained": 120," Novice": 220," Intermediate": 270," Advanced": 370," Elite": 480},
{"Body Weight":198," Untrained": 125," Novice": 230," Intermediate": 285," Advanced": 390," Elite": 505},
{"Body Weight":220," Untrained": 130," Novice": 245," Intermediate": 300," Advanced": 410," Elite": 530},
{"Body Weight":242," Untrained": 135," Novice": 255," Intermediate": 310," Advanced": 425," Elite": 550},
{"Body Weight":275," Untrained": 140," Novice": 260," Intermediate": 320," Advanced": 435," Elite": 570},
{"Body Weight":319," Untrained": 145," Novice": 270," Intermediate": 325," Advanced": 445," Elite": 580},
{"Body Weight":"320+"," Untrained": 150," Novice": 275," Intermediate": 330," Advanced": 455," Elite": 595}];

var x = 140,
    difference = 0,
    bestIndex = 0,
    bestDifference = Infinity,
    i, cur, bodyWeight;

for (i = 0; i < data.length; i++) {
    cur = data[i];
    bodyWeight = cur["Body Weight"];
    difference = Math.abs(x - bodyWeight);
    if (difference < bestDifference) {
        bestDifference = difference;
        bestIndex = i;
    }
}

console.log(data[bestIndex]);