48 lines
1.1 KiB
JavaScript
48 lines
1.1 KiB
JavaScript
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// https://javascript.info/promise-chaining
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// .then() returns a new Promise when you do "return",
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// internally calling resolve().
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new Promise(function (resolve, reject) {
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setTimeout(() => resolve(1), 1);
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}).then(function (result) {
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console.log(result);
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return result * 2;
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}).then(function (result) {
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console.log(result);
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return result * 2;
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}).then(function (result) {
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console.log(result);
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return result * 2;
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});
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/*
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It will print
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1
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2
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4
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*/
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/*
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It means that "then" is internally implemented roughly as follows:
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function then(f){
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return new Promise(function(resolve, reject) {
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resolve(f());
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})
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}
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*/
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// Another example:
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fetch('http://www.fsf.org')
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// .then below runs when the remote server responds
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.then(function (response) {
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// response.text() returns a new promise that resolves with the full response text
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// when it loads
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return response.text();
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})
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.then(function (text) {
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// ...and here's the content of the remote file
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console.log(text);
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});
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