103 lines
3.0 KiB
JavaScript
103 lines
3.0 KiB
JavaScript
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'use strict';
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var $ = require('../internals/export');
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var uncurryThis = require('../internals/function-uncurry-this');
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var toIntegerOrInfinity = require('../internals/to-integer-or-infinity');
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var thisNumberValue = require('../internals/this-number-value');
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var $repeat = require('../internals/string-repeat');
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var log10 = require('../internals/math-log10');
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var fails = require('../internals/fails');
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var $RangeError = RangeError;
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var $String = String;
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var $isFinite = isFinite;
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var abs = Math.abs;
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var floor = Math.floor;
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var pow = Math.pow;
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var round = Math.round;
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var nativeToExponential = uncurryThis(1.0.toExponential);
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var repeat = uncurryThis($repeat);
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var stringSlice = uncurryThis(''.slice);
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// Edge 17-
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var ROUNDS_PROPERLY = nativeToExponential(-6.9e-11, 4) === '-6.9000e-11'
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// IE11- && Edge 14-
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&& nativeToExponential(1.255, 2) === '1.25e+0'
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// FF86-, V8 ~ Chrome 49-50
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&& nativeToExponential(12345, 3) === '1.235e+4'
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// FF86-, V8 ~ Chrome 49-50
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&& nativeToExponential(25, 0) === '3e+1';
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// IE8-
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var throwsOnInfinityFraction = function () {
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return fails(function () {
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nativeToExponential(1, Infinity);
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}) && fails(function () {
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nativeToExponential(1, -Infinity);
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});
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};
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// Safari <11 && FF <50
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var properNonFiniteThisCheck = function () {
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return !fails(function () {
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nativeToExponential(Infinity, Infinity);
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nativeToExponential(NaN, Infinity);
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});
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};
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var FORCED = !ROUNDS_PROPERLY || !throwsOnInfinityFraction() || !properNonFiniteThisCheck();
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// `Number.prototype.toExponential` method
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// https://tc39.es/ecma262/#sec-number.prototype.toexponential
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$({ target: 'Number', proto: true, forced: FORCED }, {
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toExponential: function toExponential(fractionDigits) {
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var x = thisNumberValue(this);
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if (fractionDigits === undefined) return nativeToExponential(x);
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var f = toIntegerOrInfinity(fractionDigits);
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if (!$isFinite(x)) return String(x);
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// TODO: ES2018 increased the maximum number of fraction digits to 100, need to improve the implementation
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if (f < 0 || f > 20) throw $RangeError('Incorrect fraction digits');
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if (ROUNDS_PROPERLY) return nativeToExponential(x, f);
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var s = '';
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var m = '';
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var e = 0;
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var c = '';
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var d = '';
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if (x < 0) {
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s = '-';
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x = -x;
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}
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if (x === 0) {
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e = 0;
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m = repeat('0', f + 1);
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} else {
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// this block is based on https://gist.github.com/SheetJSDev/1100ad56b9f856c95299ed0e068eea08
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// TODO: improve accuracy with big fraction digits
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var l = log10(x);
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e = floor(l);
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var n = 0;
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var w = pow(10, e - f);
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n = round(x / w);
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if (2 * x >= (2 * n + 1) * w) {
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n += 1;
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}
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if (n >= pow(10, f + 1)) {
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n /= 10;
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e += 1;
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}
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m = $String(n);
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}
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if (f !== 0) {
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m = stringSlice(m, 0, 1) + '.' + stringSlice(m, 1);
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}
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if (e === 0) {
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c = '+';
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d = '0';
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} else {
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c = e > 0 ? '+' : '-';
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d = $String(abs(e));
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}
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m += 'e' + c + d;
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return s + m;
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}
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});
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