114 lines
3.1 KiB
JavaScript
114 lines
3.1 KiB
JavaScript
"use strict";
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// Matches paterns like '3-10'
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const RANGE_PAT = /^(\d+)-(\d+)$/;
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// Matches negative index values
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const FROM_END_PAT = /^-(\d+)$/;
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const NUM_PAT = /^-?\d+$/;
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function SmartArray(...args) {
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return new Proxy(args, {
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get: function(target, prop) {
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if (prop.match(RANGE_PAT)) {
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// Return a subarray of the elements in the specified range,
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// INCLUDING the specified end index.
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let start = parseInt(prop.replace(RANGE_PAT, "$1"));
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let end = parseInt(prop.replace(RANGE_PAT, "$2")) + 1;
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return target.slice(start, end);
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} else if (prop.match(FROM_END_PAT)) {
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// Return the element at the specified position, counting
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// back from target.length. So "-1" will refer to the last
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// element in the array.
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//
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// If the resulting index position is negative,
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// raise an exception.
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let indexFromEnd = parseInt(prop.replace(FROM_END_PAT, "$1"));
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let index = target.length - indexFromEnd;
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if (index < 0) {
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throw new Error("Index out of bounds");
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}
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return Reflect.get(target, index);
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} else {
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// Do the usual array thing -- get the value at the specified index.
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return Reflect.get(...arguments);
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}
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},
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set: function(target, prop, newVal) {
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// For smart arrays, we only allow updates to numerical fields.
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// Throw an exception for a 'prop' that is not a valid integer.
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//
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// If prop is zero or positive, update the array position normally.
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//
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// If negative, update the position counting from the end of the array.
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// However, raise an exception if the resulting index is still negative.
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if (!prop.match(NUM_PAT)) {
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throw new Error("Invalid index for assignment");
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}
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let index = parseInt(prop);
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if (index < 0) {
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index = target.length + index;
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if (index < 0) {
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throw new Error("Index out of bounds");
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}
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}
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Reflect.set(target, index, newVal);
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return true;
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},
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deleteProperty: function(target, prop) {
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if (!prop.match(NUM_PAT)) {
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throw new Error("Invalid index for deletion");
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}
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let index = parseInt(prop);
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if (index < 0) {
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index = target.length + index;
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if (index < 0) {
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throw new Error("Index out of bounds");
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}
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}
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target.splice(index, 1);
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return true;
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}
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});
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}
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let arr = SmartArray('a', 'b', 'c', 'd', 'e', 'f');
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console.log(arr[0]); // a
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console.log(arr[4]); // e
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console.log(arr['hello']); // undefined
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console.log(arr['2-4']); // [c,d,E]
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console.log(arr['3-5']); // [d,E,f]
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console.log(arr[-1]); // f
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console.log(arr[-3]); // d
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try {
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console.log(arr[-99]);
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} catch (e) {
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console.log("Exception correctly thrown.");
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}
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arr[1] = 'B';
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console.log(arr[1]); // B
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arr[-2] = 'E';
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console.log(arr[4]); // E
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try {
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arr['2-4'] = 'hello';
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} catch (e) {
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console.log("Exception correctly thrown.");
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}
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try {
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arr[3 * "hello"] = 'hello';
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} catch (e) {
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console.log("Exception correctly thrown.");
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}
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delete arr[-2];
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console.log(arr);
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