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                var num = 149600000; // 用地球到太陽的平均距離來做示範

// 數字轉科學記號
var num2scientificnotation_1 = num.toExponential();
var num2scientificnotation_2 = num.toExponential(2); // 指定小數點後留幾位數

document.write(num2scientificnotation_1 + "<br>"); // 1.496e+8
document.write(num2scientificnotation_2 + "<br>"); // 1.50e+8

// 科學記號轉數字
var scientificnotation2num_1 = Number(num2scientificnotation_1);
var scientificnotation2num_2 = Number(num2scientificnotation_2);

document.write(scientificnotation2num_1 + "<br>"); // 149600000
document.write(scientificnotation2num_2 + "<br>"); // 150000000